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Fluoxetine: Juvenile pharmacokinetics in a nonhuman primate model
Abstract
The selective serotonin reuptake inhibitor (SSRI) fluoxetine is the only psychopharmacological agent approved for use in children. While short-term studies of side effects have been performed, long-term consequences for brain development are not known. Such studies can be performed in appropriate animal models if doses modeling therapeutic use in children are known.
The goal of this study was to identify a daily dose of fluoxetine in juvenile monkeys which would result in serum fluoxetine and norfluoxetine concentrations in the therapeutic range for children.
Juvenile (2.5-year-old rhesus monkeys, n = 6) received single administration of doses of 1, 2, and 4 mg/kg day fluoxetine on a background of chronic dosing at an intermediate level to provide steady-state conditions to model therapeutic administration. Using nonlinear modeling, standard pharmacokinetic parameters were derived. Cerebrospinal fluid monoamine neurotransmitters were assayed to confirm the pharmacological effects.
Dose-dependent area under the curve (AUC) and C max values were seen, while T max and absorption/elimination half-lives were minimally influenced by dose. A dosage of 2 mg/kg day given over a 14-week period led to steady-state serum concentrations of active agent (fluoxetine + norfluoxetine) similar to those recorded from drug monitoring studies in children. Cisternal cerebrospinal fluid concentrations of serotonin increased significantly over the 14-week period, while concentrations of the serotonin metabolite (5-HIAA) were lower but not significantly different.
A dose of 2 mg/kg day fluoxetine in juvenile rhesus monkeys provides an internal dose similar to therapeutic use in children and will help establish a valuable animal model for understanding fluoxetine's therapeutic and potential adverse effects in children.
... Macaque monkeys are prominent models for childhood because of the extended juvenile period between infancy and puberty when advanced cortical functions mature under the influence of complex social systems. The review integrates findings from eight published studies of different endpoint domains (1)(2)(3)(4)(5)(6)(7)(8) with current issues in pediatric psychopharmacology. ...
... Species differences in drug metabolism can be an important barrier to translation. Studies in adult monkeys have demonstrated metabolic profiles of fluoxetine similar to those seen in humans (9)(10)(11), as did our pilot work in juvenile monkeys (1). Also, in that pilot research, fluoxetine's biological action of blocking serotonin reuptake in brain was reflected in increased concentrations of serotonin in cerebral spinal fluid after long-term treatment (1). ...
... Also, in that pilot research, fluoxetine's biological action of blocking serotonin reuptake in brain was reflected in increased concentrations of serotonin in cerebral spinal fluid after long-term treatment (1). Because simple weight-based extrapolation from humans to monkeys is not appropriate (11), preliminary pharmacokinetic studies in juvenile rhesus were used to select an oral dose of 2 mg/kg relevant to children (1). Plasma levels (fluoxetine + norfluoxetine) in the monkeys after 2 years of dosing were 273 ± 31 ng/mL (5), compared to 241 ± 91 ng/mL in children with MDD who showed a therapeutic response at the recommended dosage of 20 mg/day (12). ...
Fluoxetine therapy has been approved for children with major depressive disorder and obsessive compulsive disorder for over 14 years and has expanded to other childhood behavior disorders. As use increases, more detail on fluoxetine effects during juvenile brain development can help maintain safe and effective use of this therapy. Here, a narrative review is provided of previously published findings from a large nonhuman primate project. Fluoxetine was administered to juvenile male rhesus monkeys for an extended period (2 years) prior to puberty. Compared to controls, treated monkeys showed sleep disruption, facilitated social interaction, greater impulsivity, and impaired sustained attention during treatment. No effects on growth were seen. Metabolomics assays characterized a distinctive response to fluoxetine and demonstrated individual differences that were related to the impulsivity measure. Fluoxetine interactions with monoamine oxidase A polymorphisms that influenced behavior and metabolomics markers were an important, previously unrecognized finding of our studies. After treatment was discontinued, some behavioral effects persisted, but short-term memory and cognitive flexibility testing did not show drug effects. This detailed experimental work can contribute to clinical research and continued safe and effective fluoxetine pharmacotherapy in children.
... Genetic and environmental variables were also considered in the study. A pharmacokinetic study with multiple doses identified a dose in juvenile monkeys in the therapeutic range for children based on serum concentrations (Golub and Hogrefe, 2014a). We have previously reported that growth was not generally compromised by the treatment (Golub et al., 2015a). ...
... Fluoxetine hydrochloride, obtained as a pediatric solution (20 mg/ 5 ml, Patterson Veterinary Supply, Inc., Devens, MA), was diluted 1:1 with commercial flavored syrup or baby food for administration via an oral dosing syringe. The dose was based on a preliminary pharmacokinetic study (Golub and Hogrefe, 2014a). ...
Potential long term effects on brain development are a concern when drugs are used to treat depression and anxiety in childhood. In this study, male juvenile rhesus monkeys (three-four years of age) were dosed with fluoxetine or vehicle (N=16/group) for two years. Histomorphometric examination of cortical dendritic spines conducted after euthanasia at one year postdosing (N=8/group) suggested a trend toward greater dendritic spine synapse density in prefrontal cortex of the fluoxetine-treated monkeys. During dosing, subjects were trained for automated cognitive testing, and evaluated with a test of sustained attention. After dosing was discontinued, sustained attention, recognition memory and cognitive flexibility were evaluated. Sustained attention was affected by fluoxetine, both during and after dosing, as indexed by omission errors. Response accuracy was not affected by fluoxetine in post-dosing recognition memory and cognitive flexibility test, but formerly fluoxetine-treated monkeys compared to vehicle controls had more missed trial initiations and choices during testing. Drug treatment also interacted with genetic and environmental variables: MAOA genotype (high- and low transcription rate polymorphisms) and testing location (upper or lower tier of cages). Altered development of top-down cortical regulation of effortful attention may be relevant to this pattern of cognitive test performance after juvenile fluoxetine treatment.
... The ages of the rhesus macaque subjects in the present study (one to four years of age) correspond roughly to four to twelve year-old children. Previous reports from this project have described dose selection ( Golub and Hogrefe, 2014), metabolomic biomarkers of drug action ( He et al., 2014), bone growth ( Golub et al., 2015), sleep disturbance ( ), and social interaction ( ). Macaque monkeys have long been studied as models for emotional response during infant development ( Kalin and Shelton, 2003) and are becoming widely employed as suitable animal models for studying psychoactive drugs during juvenile and adolescent brain development ( Soto et al., 2012;Shrestha et al., 2014;Rodriguez et al., 2010;Popke et al., 2001;Paule et al., 1992;Patterson et al., 2010;Mattison et al., 2011;Mandell et al., 2011;Gill et al., 2012). ...
... Controls (N=16) received only the flavored vehicle. The fluoxetine variable corresponds to a dose of 2.0 mg/kg over the two-year treatment period, a dose based on preliminary pharmacokinetic studies ( Golub and Hogrefe, 2014), as well as previous experience with this drug in macaques ( Anderson, 2004;Clarke et al., 1999;Clarke et al., 1998;Fontenot et al., 2009;Fontenot et al., 2005;Sawyer and Howell, 2011;Shrestha et al., 2014). For 11 months prior to behavior data collection, a dose of 1.6 mg/kg was administered. ...
Juvenile male rhesus macaques received therapeutic doses of fluoxetine daily from one to three years of age and were compared to vehicle-treated controls (N=16/group). Genotyping for monoamine oxidase A (MAOA) polymorphisms was used to form subgroups (N=8) with high and low expression of the gene. Behavioral responses were scored during 30-second exposures to pictures differing in affective content. As expected from its therapeutic effect, fluoxetine decreased the behavioral response to emotionally evocative pictures. A 44% reduction in number of expressive behaviors was seen, but only in subjects with low expression MAOA polymorphisms. In general, this effect occurred for pictures of varying affective content and was not due to altered occurrence of one specific behavior or type of behavior. The drug*genotype interaction was seen after one and two years of treatment and did not reverse one year after discontinuation of dosing. Two potential translational implications are suggested: (1) MAOA genetic polymorphisms may be the source of some of the variability in response to fluoxetine treatment in children; (2) extended fluoxetine treatment during juvenile brain development may result in persistent effects on emotional regulation.
... Fluoxetine dose selection was based on information in the human and nonhuman primate literature and on a preliminary pharmacokinetic/ pharmacodynamic study to provide steady state circulating levels of fluoxetine/norfluoxetine in the range reported for therapeutic use of fluoxetine in children. 47 Dosing was initiated at 1 year of age at 1.6 mg kg − 1 per day and adjusted to 2.4 mg kg − 1 per day after 11 months. Liquid fluoxetine (20 mg per 5 ml, Webster Veterinary) was prepared for oral dosing by dilution in flavored commercial flavoring syrup (Torani). ...
... Monoamine metabolites were not assessed in the present biomarker screening study but pilot work demonstrated that 14 weeks of dosing at 2 mg kg − 1 per day significantly increased CSF serotonin and showed a trend for decrease of the serotonin metabolite 5HIAA. 47 ...
Fluoxetine is the only psychopharmacological agent approved for depression by the US Food and Drug Administration for children and is commonly used therapeutically in a variety of neurodevelopmental disorders. Therapeutic response shows high individual variability, and severe side effects have been observed. In the current study we set out to identify biomarkers of response to fluoxetine as well as biomarkers that correlate with impulsivity, a measure of reward delay behavior and potential side effect of the drug, in juvenile male rhesus monkeys. The study group was also genotyped for polymorphisms of monoamine oxidase A (MAOA), a gene that has been associated with psychiatric disorders. We used peripheral metabolite profiling of blood and cerebrospinal fluid (CSF) from animals treated daily with fluoxetine or vehicle for one year. Fluoxetine response metabolite profiles and metabolite/reward delay behavior associations were evaluated using multivariate analysis. Our analyses identified a set of plasma and CSF metabolites that distinguish fluoxetine- from vehicle-treated animals and metabolites that correlate with impulsivity. Some metabolites displayed an interaction between fluoxetine and MAOA genotype. The identified metabolite biomarkers belong to pathways that have important functions in central nervous system physiology. Biomarkers of response to fluoxetine in the normally functioning brain of juvenile nonhuman primates may aid in finding predictors of response to treatment in young psychiatric populations and in progress toward the realization of a precision medicine approach in the area of neurodevelopmental disorders.
... The fluoxetine dose resulted in serum levels seen in children treated clinically with fluoxetine. It was based on preliminary pharmacokinetic studies [88], as well as previous experience with this drug in macaques [17,[89][90][91][92][93][94]. For the first 11 months 1.6 mg/kg was administered daily. ...
Fluoxetine is an antidepressant commonly prescribed not only to adults but also to children for the treatment of depression, obsessive-compulsive disorder, and neurodevelopmental disorders. The adverse effects of the long-term treatment reported in some patients, especially in younger individuals, call for a detailed investigation of molecular alterations induced by fluoxetine treatment. Two-year fluoxetine administration to juvenile macaques revealed effects on impulsivity, sleep, social interaction, and peripheral metabolites. Here, we built upon this work by assessing residual effects of fluoxetine administration on the expression of genes and abundance of lipids and polar metabolites in the prelimbic cortex of 10 treated and 11 control macaques representing two monoamine oxidase A (MAOA) genotypes. Analysis of 8871 mRNA transcripts, 3608 lipids, and 1829 polar metabolites revealed substantial alterations of the brain lipid content, including significant abundance changes of 106 lipid features, accompanied by subtle changes in gene expression. Lipid alterations in the drug-treated animals were most evident for polyunsaturated fatty acids (PUFAs). A decrease in PUFAs levels was observed in all quantified lipid classes excluding sphingolipids, which do not usually contain PUFAs, suggesting systemic changes in fatty acid metabolism. Furthermore, the residual effect of the drug on lipid abundances was more pronounced in macaques carrying the MAOA-L genotype, mirroring reported behavioral effects of the treatment. We speculate that a decrease in PUFAs may be associated with adverse effects in depressive patients and could potentially account for the variation in individual response to fluoxetine in young people.
... Fluoxetine dose selection was based on information in the human and non-human primate literature and on a preliminary pharmacokinetic/pharmacodynamic study to provide steady-state circulating levels of fluoxetine/norfluoxetine in the range reported for therapeutic use of fluoxetine in children ( Golub and Hogrefe, 2014). Dosing was initiated at one-year of age at 1.6 mg/kg/day and adjusted to 2.4 mg/kg/day after 11 months, one month before the one-year sampling reported here. ...
We report on biochemical pathways perturbed upon chronic fluoxetine administration to juvenile macaques using global metabolomics analyses of fibroblasts derived from skin biopsies. After exposure to tissue culture conditions confounding environmental factors are eliminated and identification of metabolites whose levels are affected by the drug become apparent with a better signal-to-noise ratio compared to data obtained from plasma and cerebrospinal fluid (CSF). Levels of more than 200 metabolites were analyzed to interrogate affected molecular pathways and identify biomarkers of drug response. In addition, we have correlated the metabolomics results with monoamine oxidase (MAOA) genotype and impulsivity behavioral data. Affected pathways include Purine and Pyrimidine metabolisms that have been previously implicated to contribute to neuropsychiatric disorders.
... Monkeys came forward for dosing, the syringe was emptied into their mouth followed by a "chaser" to ensure swallowing. A therapeutic fluoxetine dose of 2 mg/kg/day was based on literature from children and macaque monkeys and on an acute pharmacokinetic/pharmacodynamic study to confirm internal dose [37]. Dosing was initiated at one year of age at 1.6 mg/kg/day while animals were adjusting to indoor housing and syringe dosing and adjusted to 2.4 mg/kg/day after 11 months. ...
Male rhesus monkeys received a therapeutic oral dose of the selective serotonin reuptake inhibitor (SSRI) fluoxetine daily from 1 to 3years of age. Puberty is typically initiated between 2 and 3years of age in male rhesus and reproductive maturity is reached at 4years. The study group was genotyped for polymorphisms in the monoamine oxidase A (MAOA) and serotonin transporter (SERT) genes that affect serotonin neurotransmission. Growth was assessed with morphometrics at 4month intervals and radiographs of long bones were taken at 12month intervals to evaluate skeletal growth and maturation. No effects of fluoxetine, or MAOA or SERT genotype were found for growth during the first year of the study. Linear growth began to slow during the second year of the study and serotonin reuptake transporter (SERT) long polymorphic region (5HTTLPR) polymorphism effects with drug interactions emerged. Monkeys with two SERT 5HTTLPR L alleles (LL, putative greater transcription) had 25-39% less long bone growth, depending on the bone, than monkeys with one S and one L allele (SL). More advanced skeletal maturity was also seen in the LL group, suggesting earlier onset of puberty. An interaction between 5HTTLPR polymorphisms and fluoxetine was identified for femur and tibia growth; the 5HTTLPR effect was seen in controls (40% less growth for LL) but not in the fluoxetine treated group (10% less growth for LL). A role for serotonin in peripubertal skeletal growth and maturation has not previously been investigated but may be relevant to treatment of children with SSRIs.
Copyright © 2015. Published by Elsevier Inc.
The ability to deliver drugs with precise dosages at specific time points can significantly improve disease treatment while reducing side effects. Drug encapsulation for gradual delivery has opened the doors for a superior treatment regimen. To expand on this ability, programming bioelectronic devices to deliver small molecules enables ad‐hoc personalized therapeutic profiles that are more complex than gradual release. Here, a wearable bioelectronic device with an integrated electrophoretic ion pump that affords on‐demand drug delivery with precise dose control is introduced. Delivery of fluoxetine to wounds in mice result in a 27.2% decrease in the macrophage ratio (M1/M2) and a 39.9% increase in re‐epithelialization, indicating a shorter inflammatory phase and faster overall healing. Programmable drug delivery using wearable bioelectronics in wounds introduces a broadly applicable strategy for the long‐term delivery of a prescribed treatment regimen with minimal external intervention.
Sleep disturbance is a reported side effect of antidepressant drugs in children. Using a nonhuman primate model of childhood selective serotonin reuptake inhibitor (SSRI) therapy, sleep was studied quantitatively with actigraphy. Two 48-h sessions were recorded in the home cage environment of juvenile male rhesus monkeys at two and three years of age, after one and two years of treatment with a therapeutic dose of the SSRI fluoxetine, and compared to vehicle treated controls. A third session was conducted one year after discontinuation of treatment at four years of age. During treatment, the fluoxetine group demonstrated sleep fragmentation as indexed by a greater number of rest-activity transitions compared to controls. In addition fluoxetine led to more inactivity during the day as indexed by longer duration of rest periods and the reduced activity during these periods. The fluoxetine effect on sleep fragmentation, but not on daytime rest, was modified by the monkey's genotype for polymorphisms of monoamine oxidase A (MAOA), an enzyme that metabolizes serotonin. After treatment, the fluoxetine effect on nighttime rest-activity transitions persisted, but daytime activity was not affected. The demonstration in this nonhuman primate model of sleep disturbance in connection with fluoxetine treatment and specific genetic polymorphisms, and in the absence of diagnosed psychopathology, can help inform use of this drug in children.
Background:
Fluoxetine improves social interactions in children with autism, social anxiety and social phobia. It is not known whether this effect is mediated directly or indirectly by correcting the underlying pathology. Genetics may also influence the drug effect. Polymorphisms of the MAOA (monoamine oxidase A) gene interact with fluoxetine to influence metabolic profiles in juvenile monkeys. Juvenile nonhuman primates provide an appropriate model for studying fluoxetine effects and drug*gene interactions in children.
Methods:
Male rhesus monkeys 1-3 years of age living in permanent social pairs were treated daily with a therapeutic dose of fluoxetine or vehicle (n=16/group). Both members of each social pair were assigned to the same treatment group. They were observed for social interactions with their familiar cagemate over a 2-year dosing period. Subjects were genotyped for MAOA variable number of tandem repeats (VNTR) polymorphisms categorized for high or low transcription rates (hi-MAOA, low-MAOA).
Results:
Fluoxetine-treated animals spent 30% more time in social interaction than vehicle controls. Fluoxetine significantly increased the duration of quiet interactions, the most common type of interaction, and also of immature sexual behavior typical of rhesus in this age group. Specific behaviors affected depended on MAOA genotype of the animal and its social partner. When given fluoxetine, hi-MOAO monkeys had more social invitations and initiation behaviors and low-MAOA subjects with low-MAOA partners had more grooming and an increased frequency of some facial and vocal expressive behaviors.
Conclusions:
Fluoxetine may facilitate social interaction in children independent of remediation of psychopathology. Common genetic variants may modify this effect.
Objective:
This study examined the long-term effects of fluoxetine administered to juvenile rhesus monkeys who, as young adults, were imaged with positron emission tomography for two serotonergic markers: serotonin transporter (SERT) and serotonin 1A (5-HT1A) receptor. An equal number of monkeys separated from their mothers at birth-an animal model of human childhood stress-were also studied.
Method:
At birth, 32 male rhesus monkeys were randomly assigned to either maternal separation or normal rearing conditions. At age 2, half (N=8) of each group was randomly assigned to fluoxetine (3 mg/kg) or placebo for 1 year. To eliminate the confounding effects of residual drug in the brain, monkeys were scanned at least 1.5 years after drug discontinuation. Social interactions were assessed both during and after drug administration.
Results:
Fluoxetine persistently upregulated SERT, but not 5-HT1A receptors, in both the neocortex and the hippocampus. Whole-brain voxel-wise analysis revealed that fluoxetine had a significant effect in the lateral temporal and cingulate cortices. In contrast, neither maternal separation by itself nor the rearing-by-drug interaction was significant for either marker. Fluoxetine had no significant effect on the behavioral measures.
Conclusions:
Fluoxetine administered to juvenile monkeys upregulates SERT into young adulthood. Implications regarding the efficacy or potential adverse effects of SSRIs in patients cannot be directly drawn from this study. Its purpose was to investigate effects of SSRIs on brain development in nonhuman primates using an experimental approach that randomly assigned long-term SSRI treatment or placebo.
The short-term effects on rates and durations of self-injurious behavior and self-directed stereotypies associated with various doses of fluoxetine (FLX) and venlafaxine (VEN) were examined in rhesus macaques. Adult male macaques (Macaca mulatta; n = 17; age, 7 to 15 y) with at least 1 episode of severe SIB within the past 5 y were randomized to treatment with FLX (n = 6), VEN (n = 6), or placebo (PLC, n = 5), administered by voluntary consumption of medication provided in fruit-flavored tablets. After 4-wk baseline and 4-wk placebo lead-in phases, doses were increased monthly for 4 mo (FLX: 0.5, 2.0, 4.0, and 8.0 mg/kg; VEN: 2.0, 4.0, 8.0, and 16.0 mg/kg). Animals in the PLC condition received similar nonmedicated fruit-flavored tablets. Focal behavioral observations, plasma drug levels, and neurochemical data were obtained. Results indicated that rates and percentage time spent self-biting declined at all doses of FLX, with the greatest effect seen at 2.0 mg/kg. For VEN, percentage time spent self-biting was significantly lower only at the 4.0 mg/kg dose. Treatment-induced reductions in platelet serotonin and cerebrospinal fluid 5-hydroxyindoleacetic acid (CSF 5HIAA) concentrations were substantially greater in the FLX-treated condition than in the VEN-treated condition. Plasma FLX and norfluoxetine levels increased with FLX dose; plasma levels of VEN were low and not dose-related. Fluoxetine at a dose of 2.0 mg/kg daily was most efficacious in reducing SIB, and the observed reductions in platelet serotonin and CSF 5HIAA levels indicated substantial bioeffect at this dose. Treatment with VEN was marked by noncompliance, low bioeffect, and low efficacy.
Monoamine oxidase A (MAOA), a mitochondrial enzyme involved in the degradation of biogenic amines, may be implicated in the pathogenesis of major depressive disorder (MDD) and be related to the therapeutic effects of antidepressants. To elucidate a genetic predisposition of MDD, we studied a variable-number-tandem-repeat (VNTR) polymorphism in the promoter region of the MAOA gene in a Chinese population of 230 MDD patients and 217 controls. We also examined the association of this polymorphism and antidepressant therapeutic response in the MDD patients who underwent a 4-week fluoxetine treatment. Our results showed a significantly increased frequency of 4-repeat (4R) allele in MDD patients, especially in the female population. Furthermore, MDD female patients who were 3R homozygotes had a significantly better response to 4-week fluoxetine treatment when compared to 4R carriers (p=0.024), but there was a nonsignificant difference found in male patients (p=0.081). Since the 4R allele transcribed 2-10 times more efficiently than those with 3R allele, our findings suggest that the MAOA-uVNTR may be involved in the pathogenesis of MDD and the antidepressant therapeutic mechanisms in Chinese population, and that there may be a gender effect in this association.
ABSTRACT– In an open study of depressed inpatients, the effects of the selective serotonin uptake blocker fluoxetine on 5-hydroxyindoleacetic acid (5-HIAA), homo-vanillic acid (HVA), 4-hydroxy-3-methoxyphenyl glycol (HMPG) and N-terminally extended substance P (SP) in cerebrospinal fluid (CSF) were measured. Thirteen unmedicated patients who met the DSM-III criteria for major depressive episode were included, and 9 completed the study. During treatment the 5-HIAA concentration decreased by 46%. The HVA and HMPG concentrations also decreased significantly, but to a lesser degree. The mean level of N-terminally extended SP was unaffected by fluoxetine treatment, but the pretreatment level correlated significantly with the pretreatment level of HMPG. The pretreatment level of HVA was the only biochemical variable that appeared to predict therapeutic outcome. The plasma concentrations of both fluoxetine and its metabolite norfluoxetine increased significantly between 3 and 6 weeks. Plasma and CSF levels of both the parent drug and its active metabolite were correlated.
Although fluoxetine is useful in the treatment of major depression, 30-40 % of the patients do not respond to therapy. The response seems to be influenced by certain genes which are involved in the drug's pharmacodynamics and pharmacokinetics. The present study reviews the literature on genetic contributions to fluoxetine response in children and adults, and concludes that the different polymorphisms of CYP2D6 and CYP2C9 may influence the blood concentrations of fluoxetine. If the childhood dose is adjusted for weight, differences between children and adults are unlikely. As regards the genes that influence the drug's pharmacodynamics, polymorphisms of SLC6A4, HTR1A and MAO-A seem to be involved in the response to fluoxetine, while the genes COMT, CRHR1, PDEA1, PDEA11 GSK3B and serpin-1 also seem to play a role. Comparison of different studies reveals that the results are not always consistent, probably due to methodological differences. Other factors such as gender or ethnicity may also influence treatment response.
Social and emotional behaviors are known to be sensitive to both developmental iron deficiency (ID) and monoamine oxidase A (MAOA) gene polymorphisms. In this study, male rhesus monkey infants deprived of dietary iron in utero were compared with iron sufficient (IS) controls (n = 10/group). Half of each group had low MAOA activity genotypes and half had high MAOA activity genotypes. A series of social response tests were conducted at 3-14 months of age. MAOA genotype influenced attention to a video of aggressive behavior, emotional expression (fear, grimace and sniff) in the social intruder test, social actions (displacement, grooming) in the social dyad test, and aggressive responses to a threatening picture. Interactions between MAOA and prenatal ID were seen in response to the aggressive video, in temperament ratings, in affiliative behavior in the social dyad test, in cortisol response in the social buffering test and in response to a social intruder and to pictures with social and nonsocial themes. In general, the effects of ID were dependent on MAOA genotype in terms of both direction and size of the effect. Nutrition/genotype interactions may shed new light on behavioral consequences of nutritional deprivation during brain development.
Information about therapeutic serum levels of fluoxetine (FLX) and its major metabolite norfluoxetine (NORFLX) in children and adolescents is scarce.
Therapeutic drug monitoring (TDM) of FLX was routinely performed in 71 subjects treated for a major depressive disorder (MDD) (10-60 mg/d FLX, median: 20 mg/d). Correlations between serum concentration and dosage, age, gender, smoking habits and adverse events were analysed.
Serum concentrations of the active moiety (FLX + NORFLX) ranged from 21 to 613 ng/mL (mean concentration of 213 ± 118 ng/mL, median: 185 ng/mL). High inter-individual variability in serum concentrations of the active moiety of FLX at each dosage level was observed and no relationship between serum concentration and clinical outcome was found. Apart from smoking, none of the factors tested had a significant eff ect on the serum concentration.
It was shown that serum concentrations of the active moiety of FLX in children and adolescents seem to be similar to those in adults, with a high level of inter-individual variation. The proportion of patients who showed benefits from treatment with a dose of 20 mg/d FLX was high.
Fluoxetine (Prozac) is a selective serotonin reuptake inhibitor currently used to treat depression and mood disorders. It has been widely studied clinically and preclinically, yet there is limited knowledge of its pharmacokinetics in nonhuman primates.
The present study characterized the pharmacokinetics of fluoxetine and its active metabolite norfluoxetine in rhesus macaques following both acute (1, 3, 5.6 and 10 mg/kg) and chronic doses (5.6 and 10 mg/kg/day) via different routes of administration (intravenous, subcutaneous, intramuscular, and oral). Blood samples were collected at multiple time points following administration and analyzed using mass spectrometry.
Fluoxetine had a half-life of 11-16 h and norfluoxetine had a half-life of 21-29 h. Potentially functionally significant serum concentrations of norfluoxetine were present at 24 h even after a single administration of fluoxetine. Similar to observations in humans under steady state conditions, norfluoxetine accounted for the greater percentage of active drug in the blood stream.
A daily dose of 10 mg/kg administered orally maintained serum concentrations in the human clinical range over the course of 6 weeks. Given the long half-lives of fluoxetine and norfluoxetine observed in this study, precautions should be taken when designing preclinical studies to prevent accumulation of drug serum concentrations.
By conferring allele-specific transcriptional activity on the 5-HT transporter gene promoter in humans, the 5-HT transporter gene-linked polymorphic region (5-HTTLPR) influences a constellation of personality traits related to anxiety and increases the risk for neurodevelopmental, neurodegenerative, and psychiatric disorders. Here we have analyzed the presence and variability of the 5-HTTLPR in several species of primates including humans, and other mammals. PCR, Southern blot, and sequence analyses of the 5-HT transporter gene's 5'-flanking region in different mammalian species confirmed the presence of the 5-HTTLPR in platyrrhini and catarrhini (hominoids, cercopithecoids) but not in prosimian primates and other mammals. Since the 5-HTTLPR is unique to humans and simian primates, a progenitor 5-HTTLPR sequence may have been introduced into the genome some 40 Mio, years ago. In humans the majority of alleles are composed of either 14 or 16 repeat elements, while alleles with 18 or 20 repeat elements are rare. In contrast, great apes including orang-utan, gorilla, and chimpanzee display a high prevalence of alleles with 18 and 20 repeat elements. In hominoids all alleles originate from variation at a single locus (polymorphic locus 1). In the 5-HTTLPR of rhesus monkeys (rh5-HTTLPR) we found an alternative locus for length variation (polymorphic locus 2) generated by a 21 bp insertion/deletion event. The existence of a distinct biallelic variation of the 5-HTTLPR in rhesus monkeys but similar allele and genotype frequencies in this species and humans supports the notion that there may be a relationship between functional 5-HT transporter expression, anxiety-related traits, and the complexity of socialization in human and non-human primate populations.
The human cytochrome P450 2D6 (CYP2D6) is a primary enzyme involved in the metabolism of about 25% of commonly used therapeutic drugs. CYP2D6 belongs to the CYP2D subfamily, a gene cluster located on chromosome 22, which comprises the CYP2D6 gene and pseudogenes CYP2D7P and CYP2D8P. Although the chemical and physiological properties of CYP2D6 have been extensively studied, there has been no study to date on molecular evolution of the CYP2D subfamily in the human genome. Such knowledge could greatly contribute to the understanding of drug metabolism in humans because it makes us to know when and how the current metabolic system has been constructed. The knowledge moreover can be useful to find differences in exogenous substrates in a particular metabolism between human and other animals such as experimental animals. Here, we conducted a preliminary study to investigate the evolution and gene organization of the CYP2D subfamily, focused on humans and four non-human primates (chimpanzees, orangutans, rhesus monkeys, and common marmosets). Our results indicate that CYP2D7P has been duplicated from CYP2D6 before the divergence between humans and great apes, whereas CYP2D6 and CYP2D8P have been already present in the stem lineages of New World monkeys and Catarrhini. Furthermore, the origin of the CYP2D subfamily in the human genome can be traced back to before the divergence between amniotes and amphibians. Our analyses also show that reported chimeric sequences of the CYP2D6 and CYP2D7 genes in the chimpanzee genome appear to be exchanged in its genome database.
A rapid, sensitive and selective bioanalytical method was developed for the simultaneous determination of fluoxetine and its primary metabolite norfluoxetine in human plasma. Sample preparation was based on supported liquid extraction (SLE) using methyl tert-butyl ether to extract the analytes from human plasma. Chromatography was performed on a Synergi 4 μ polar-RP column using a fast gradient. The ionization was optimized using ESI (+) and selectivity was achieved by tandem mass spectrometric analysis using MRM functions, m/z 310 → 44 for fluoxetine, m/z 296 → 134 for norfluoxetine and m/z 315 → 44 for fluoxetine-d(5) (internal standard). The method is linear over the range of 0.05-20 ng/mL (using a human plasma sample volume of 0.1 mL) with a coefficient determination of greater than 0.999. The method is accurate and precise with intra-batch and inter-batch accuracy (%bias) of <±15% and precision (%CV) of <15% for both analytes. A run time of 4 min means a high throughput of samples can be achieved. To our knowledge, this method appears to be the most sensitive one reported so far for the quantitation of fluoxetine and norfluoxetine and can be used for routine therapeutic drug monitoring or pharmacokinetic studies. Copyright © 2011 John Wiley & Sons, Ltd.
Disturbances in central serotonin function have been implicated in impulsive and aggressive behavior. A deletion/insertion polymorphism within the 5-HT transporter promoter gene (5-HTTLPR) is thought to be associated with disturbed impulse control, anxiety, and depression. The serotonin transporter (5-HTT) is the primary action site for selective serotonin reuptake inhibitors (SSRIs). Several studies of major depression have shown that the l allele of 5-HTTLPR is associated with better SSRI antidepressant effects than the s allele.
This study investigates the association between response of impulsivity to treatment with fluoxetine and 5-HTTLPR polymorphism in 49 personality disordered patients. Additionally, we studied TPH1, 5HT1B and 5HT2C receptor polymorphisms as predictors of response in this population.
Results reveal that patients with the l/l genotype of 5-HTTLPR had a significantly better response to fluoxetine when compared to s allele carriers, as evaluated on the basis of total (P<0.05) and Aggression subscale (P<0.01) Overt Aggression Scale Modified-score percentage change. There were no significant associations between fluoxetine response and TPH1 (A218C) (-6525 A>G) (-5806 G>T), HTR1B (G861C) and HTR2C (G68C) genotype groups.
This is the first study assessing the association between these polymorphisms and anti-impulsive response to fluoxetine in personality disorder. As the s genotype is associated with a poorer selective serotonin reuptake inhibitors response in major depression, bulimia nervosa and borderline personality disorder, it could represent a common biological background for SSRI response.
Norfluoxetine is the most important active metabolite of the widely used antidepressant fluoxetine. Although the pharmacokinetics/pharmacodynamics (PK/PD) relationship and neurochemical profile of fluoxetine is well characterized in human and in animals, little is known about the effect of its metabolite. The aim of this study was to characterize extracellular level of serotonin (5-hydroxytryptamine, 5-HT)-time profile of norfluoxetine after acute administration over 18 h post dose and to establish the relationship between this pharmacodynamic (PD) profile and its pharmacokinetic (PK) properties. Following subcutaneous administration of fluoxetine in rats, plasma and brain PK of fluoxetine and norfluoxetine were monitored respectively by liquid chromatography/tandem mass spectrometry (LC/MS/MS). The extracellular level of 5-HT in the frontal cortex was measured by microdialysis as a PD endpoint. Norfluoxetine when directly administrated to rats caused a significant increase in extracellular level of 5-HT in the frontal cortex and maintained for 18 h. This result is correlated well with higher plasma and brain concentration and longer plasma and brain retention time of norfluoxetine. Our results showed that norfluoxetine contributes to 5-HT transporter inhibition and extends fluoxetine efficacy.
The pharmacokinetic properties of the newer specific serotonin (5-HT) reuptake inhibitors are reviewed. Fluoxetine, paroxetine, sertraline, and fluvoxamine show kinetic characteristics similar to those of the older tricyclic antidepressants. They are well absorbed orally but exhibit an extensive first-pass extraction in the liver. They are widely distributed in body tissues and highly bound to plasma proteins. The clearance of these drugs by the body is accomplished almost entirely by hepatic metabolism. Fluoxetine and sertraline both produce a pharmacologically active metabolite, although insufficient data are available to evaluate the clinical significance of desmethylsertraline. With the exception of fluoxetine, which has an elimination half-life of 2 to 3 days, the other drugs have half-lives of about 1 day. Available data indicate that paroxetine and fluvoxamine achieve steady state within 4 to 14 days of chronic dosing, whereas for fluoxetine, and particularly norfluoxetine, steady state is not reached for weeks. The pharmacokinetics of these drugs are characterized by marked intersubject variability. Only preliminary data are available on steady-state plasma concentrations achieved during treatment and correlations to therapeutic or adverse effects.
In an open study of depressed inpatients, the effects of the selective serotonin uptake blocker fluoxetine on 5-hydroxyindoleacetic acid (5-HIAA), homovanillic acid (HVA), 4-hydroxy-3-methoxyphenyl glycol (HMPG) and N-terminally extended substance P (SP) in cerebrospinal fluid (CSF) were measured. Thirteen unmedicated patients who met the DSM-III criteria for major depressive episode were included, and 9 completed the study. During treatment the 5-HIAA concentration decreased by 46%. The HVA and HMPG concentrations also decreased significantly, but to a lesser degree. The mean level of N-terminally extended SP was unaffected by fluoxetine treatment, but the pretreatment level correlated significantly with the pretreatment level of HMPG. The pretreatment level of HVA was the only biochemically variable that appeared to predict therapeutic outcome. The plasma concentrations of both fluoxetine and its metabolite norfluoxetine increased significantly between 3 and 6 weeks. Plasma and CSF levels of both the parent drug and its active metabolite were correlated.
Drugs are discovered by a variety of approaches, which include a systematic evaluation of synthetic compounds, using extensive structure activity relationships. After a lead compound which possesses desirable pharmacological properties is found, through the exhaustive screening of a variety of compounds, a number of congeners are then synthesised and tested, using specific physiological or biochemical models of therapeutic agents. The discovery of fluoxetine involved this complex process, and led to the description in the literature of one of the first selective serotonin uptake inhibitors (Wong et al , 1974); it was subsequently tested clinically, and these studies demonstrated its effectiveness and safety as an antidepressant drug (Chouinard, 1985). This paper reviews the published information relevant to fluoxetine's pharmacology and pharmacokinetics in man.
This paper describes the effect of the selective serotonin reuptake inhibiting drug (SSRI), paroxetine, on cerebrospinal fluid concentrations of neurotransmitter metabolites in depressed patients. 5-Hydroxyindoleacetic acid (5-HIAA), 3-methoxy-4-hydroxyphenylglycol (MHPG) and homovanillic acid (HVA) were measured at baseline and after 3 weeks of treatment with 30 mg paroxetine daily. In line with similar studies on other SSRIs, influence on both the serotonin and noradrenaline metabolite was found. The mechanism behind the action of paroxetine on both 5-HIAA and MHPG is assumed to be an expression of the linkage between the serotonergic and noradrenergic systems in the brain. A frequently reported correlation between 5-HIAA and HVA was also found. The analysis of paroxetine in CSF proves the transportation of the drug into the central nervous system.
Cerebrospinal fluid (CSF) levels of the monoamine metabolites 5-hydroxyindoleacetic acid (5-HIAA), 3-methoxy-4-hydroxyphenylglycol (MHPG), and homovanillic acid (HVA) were measured in three groups: 46 healthy volunteers; 9 medication-free patients with DSM III-R major depressive disorder, recurrent; and these same 9 patients following at least 4 weeks of fluoxetine treatment at 20 mg/day. CSF monoamine metabolite levels in medication-free patients did not differ from healthy volunteers; however, CSF 5-HIAA and MHPG decreased significantly from 95.9 +/- 24.6 (all values +/- SD) to 64.2 +/- 26.1 pmol/ml and from 46.7 +/- 14.2 to 42.6 +/- 11.6 pmol/ml, respectively, following fluoxetine treatment. Fluoxetine also significantly decreased mean Hamilton Depression Rating Scale scores from 23.2 +/- 6.5 to 17.4 +/- 5.0 and significantly increased the CSF HVA/5-HIAA ratio.
The article focuses on the effects of the serotonin selective reuptake inhibitors (SSRIs) on specific drug metabolizing isoenzymes: CYP2D6, CYP3A3/4, CYP1A2, CYP2C9, and CYP2C19. Both in vitro and in vivo data regarding the inhibition potential of the SSRIs at each of these isoenzyme systems are reviewed. In general, the magnitude of the in vivo interactions between the SSRIs and substrates for these isoenzyme systems mirrors to a large extent their in vitro inhibitory potencies. However, in vitro work is limited owing to pharmacokinetic considerations, the effect of metabolites on the isoenzymes, and the likelihood that several isoenzymes are co-responsible for the metabolism of a substrate.
We sought to determine whether fluvoxamine and fluoxetine, two different antidepressants with in vitro selectivity for the serotonin uptake transporter also demonstrated similar selectivity in vivo. To accomplish this, we measured cerebrospinal fluid (CSF) concentrations of 5-hydroxyindoleacetic acid (5-HIAA), 3-methoxy-4-hydroxyphenylglycol (MHPG), and homovanillic acid (HVA) before and after 6 weeks of treatment with these two drugs. Twenty-four subjects who had major depression according to DSM-III-R criteria gave written, informed consent for the collection of CSF during a double-blind comparative treatment trial of fluvoxamine (50-150 mg/day) and fluoxetine (20-80 mg/day). The symptoms of subjects were assessed clinically on a weekly basis throughout the treatment trial. CSF samples were obtained after a 7- to 14-day washout period before treatment and again at the end of treatment. CSF samples were analyzed for 5-HIAA, HVA, and MHPG using high-pressure liquid chromatography coupled to electrochemical detection. Fluvoxamine- and fluoxetine-treated patients did not differ in clinical outcome or in the CSF concentrations of monoamine metabolite levels before or after treatment. Therefore, the CSF data were pooled. Drug treatment, overall, was associated with significant decreases in 5-HIAA and MHPG and a trend toward a reduction in HVA levels. Levels of 5-HIAA, MHPG, and HVA were reduced by 57%, 48%, and 17%, respectively. In addition, the magnitude of the decreases in 5-HIAA and MHPG appeared to be correlated (r = 0.83) across the subjects, although a Spearman rank correlation indicated that outlying values had an undue effect on this relationship. These results suggest that treatment with selective serotonin reuptake inhibitors, which are selective for serotonin uptake in vitro, does not show a similarly selective effect on serotonin in vivo during treatment of patients.
Pharmacokinetic interactions of clozapine and its metabolites N-desmethylclozapine and clozapine N-oxide with the selective serotonin reuptake inhibitors (SSRIs) fluvoxamine and paroxetine were investigated in a prospective study in schizophrenic patients under steady-state conditions. Thirty patients were treated with clozapine at a target dose of 2.5 to 3.0 mg/kg of body weight. After gradual dose escalation, serum concentrations of clozapine and two metabolites were determined twice at 7-day intervals after steady-state conditions had been reached. Then, fluvoxamine (50 mg/day) or paroxetine (20 mg/day) was added in 16 and 14 patients, respectively. Serum concentrations of clozapine and its metabolites were measured after 1, 7, and 14 days of coadministration with the SSRI. Mean trough concentrations of steady-state serum concentrations of clozapine, N-desmethylclozapine, and clozapine N-oxide were markedly elevated under fluvoxamine by about threefold of baseline concentrations whereas paroxetine induced only minor, nonsignificant changes. Estimation of the mean elimination half-life of clozapine 2 weeks after start of fluvoxamine comedication revealed an increase from 17 hours to about 50 hours whereas there was no change under paroxetine coadministration. The N-desmethylclozapine/clozapine ratio did not change significantly with either SSRI. Under monotherapy, clozapine mean serum concentrations in smokers were significantly lower by 32% compared with nonsmokers. Similarly, N-demethylation ratios were about 20 to 50% higher in smokers. Thus, in all patients, fluvoxamine induced relevant increases in serum concentrations of clozapine and its metabolites, probably by the inhibition of enzymes catalyzing the degradation of clozapine and N-desmethylclozapine, whereas paroxetine, at a usual clinically effective dosage of 20 mg/day, did not cause significant pharmacokinetic interactions.
Normal hypothalamic-pituitary-adrenal (HPA) axis activity is disrupted in several types of human psychiatric disorders, and has been widely reported to be altered as a result of early experience in rodents. In this study the effects of early social experience on later response of the HPA axis to separations from cagemates and pharmacologic treatments were examined in rhesus monkeys. HPA axis activity was measured in mother-reared and peer-reared monkey infants in conjunction with six repeated separations from and reunions with their cagemates. Within each rearing group, infants were assigned to one of three treatment groups that received continuous treatment with either fluoxetine (2 mg/kg), desipramine (DMI, 5 mg/kg) or placebo (saline) beginning 2 weeks prior to separations. At 2 weeks after drug treatment, fluoxetine increased ACTH and cortisol in the treated groups, while DMI decreased ACTH and cortisol in both treated groups; however, these effects were not persistent over the separations. While these treatment effects tended to be more pronounced in the mother-reared group, the rearing groups did not show a clearly differential response to either of the treatments. The most prominent finding was that mother-reared monkeys showed significantly higher ACTH and cortisol levels than peer-reared monkeys over all samples, an effect that may have mitigated a potential rearing group difference in treatment response. The results add to growing evidence for the influence of primate mothers on the functional development of psychobiological systems in their infants, and suggest that the HPA axis is among the more sensitive of these systems to postnatal experience.
It has been hypothesized that adverse early experience may be a mechanism by which children become vulnerable to later psychopathology via alteration of neurochemical or hormonal systems associated with such disorders. Such effects may in turn affect later responses to pharmacologic agents that act on these systems.
In this study, 18 mother-reared (MR) and 18 peer-reared (PR) rhesus monkeys experienced six 1-week separations from cagemates interspersed with 1-week reunions, while housed in like-reared groups of 3. Within rearing groups, equal numbers of animals received either fluoxetine (2 mg/kg), desipramine (5 mg/kg) or placebo delivered daily beginning 4 weeks before the first separation. Levels of norepinephrine (NE), the NE metabolite MHPG, the dopamine metabolites DOPAC and HVA, and the serotonin metabolite 5HIAA were measured in CSF samples collected approximately every 2 to 3 weeks during these procedures.
Following treatment, DMI increased NE and decreased MHPG in the DMI-treated groups, while 5HIAA was decreased in the fluoxetine-treated groups following treatment. The increase in NE was followed by a sharp decline over the course of treatment, which was accompanied by an increase in MHPG. The rearing groups did not show a differential response to the drug treatments, and the separation manipulation itself had few effects. The mother-reared group showed higher levels of NE and DOPAC over all samples and higher levels of HVA in most samples.
These rearing effects on biogenic amine activity were observed even in the presence of pharmacologic treatments that effectively altered the activity of these systems, and are consistent with previous findings from the same subject. The higher NE values observed in mother-reared infants over separations and reunions may have been due to higher basal levels of NE than peer-reared monkeys or to greater responsiveness to the stress of repeated social disruption or both. These findings agree with other primate studies showing that rearing differences persist beyond the infancy period and add to growing evidence of the important influence of the early social environment on neurobiologic development in primates.
The authors report the CYP2D6 inhibitory effects of fluoxetine, paroxetine, sertraline, and venlafaxine in an open-label, multiple-dose, crossover design. Twelve CYP2D6 extensive metabolizers were phenotyped, using the dextromethorphan/dextrorphan (DM/DX) urinary ratio, before and after administration of fluoxetine 60 mg (loading dose strategy), paroxetine 20 mg, sertraline 100 mg, and venlafaxine 150 mg. Paroxetine, sertraline, and venlafaxine sequences were randomized with 2-week washouts between treatments; fluoxetine was the last antidepressant (AD) administered. Comparing within groups, baseline DM/DX ratios (0.017) were significantly lower than DM/DX ratios after treatment (DM/DXAD) with fluoxetine (0.313, p < 0.0001) and paroxetine (0.601, p < 0.0001) but not for sertraline (0.026, p = 0.066) or venlafaxine (0.023, p = 0.485). Between groups, DM/DXAD ratios were significantly higher for fluoxetine and paroxetine compared to sertraline and venlafaxine. No differences between DM/DXAD ratios were found for fluoxetine and paroxetine although more subjects phenocopied to PM status after receiving the latter (42% vs. 83%; chi 2 = 4.44, p = 0.049, df = 1). Similarly, no differences between DM/DXAD ratios were found for sertraline and venlafaxine. Of note, the DM/DXAD for 1 subject was much lower after treatment with paroxetine (0.058) compared to fluoxetine (0.490), while another subject exhibited a much lower ratio after treatment with fluoxetine (0.095) compared to paroxetine (0.397). Significant correlations between AD plasma concentration and DM/DXAD were found for paroxetine (r2 = 0.404, p = 0.026) and sertraline (r2 = 0.64, p = 0.002) but not fluoxetine or venlafaxine. In addition, DM/DXAD correlated with baseline isoenzyme activity for paroxetine, sertraline, and venlafaxine groups. These results demonstrate the potent, but variable, CYP2D6 inhibition of fluoxetine and paroxetine compared to sertraline and venlafaxine. CYP2D6 inhibition may be related, in part, to dose, plasma concentration, and baseline isoenzyme activity, and these correlations merit further investigation.
The five selective serotonin reuptake inhibitors (SSRIs), fluoxetine, fluvoxamine, paroxetine, sertraline, and citalopram, have similar antidepressant efficacy and a similar side effect profile. They differ, however, in their pharmacokinetic properties. Under steady-state concentrations, their half-lives range between 1 and 4 days for fluoxetine (7 and 15 days for norfluoxetine) and between 21 (paroxetine) and 36 (citalopram) hr for the other SSRIs. Sertraline and citalopram show linear and fluoxetine, fluvoxamine, and paroxetine nonlinear pharmacokinetics. SSRIs underlie an extensive metabolism with high interindividual variability, whereby cytochrome P450 (CYP) isoenzymes play a major role. Therefore, resulting blood concentrations are highly variable between individuals. Except for N-demethylated fluoxetine, metabolites of SSRIs do not contribute to clinical actions. Therapeutically effective blood concentrations are unclear so far, although there is evidence for minimal effective and upper-threshold concentrations that should not be exceeded. Paroxetine and, to a lesser degree, fluoxetine and norfluoxetine are potent inhibitors of CYP2D6 and fluvoxamine of CYP1A2 and CYP2C19. This can give rise to drug-drug interactions that may have no effect, lead to intoxication, or improve the therapeutic response. These different pharmacokinetic properties of the five SSRIs, especially their drug-drug interaction potential, should be considered when selecting a distinct SSRI for treatment of depression or other disorders with a suggested dysfunction of the serotonergic system in the brain.
Antidepressants are widely used in treating depression and other behavioral problems in children and adolescents. Little is known about the long-term effects of these agents, particularly on physiological systems. The effects of previous antidepressant treatment during a social challenge in 9-month-old rhesus monkeys (Macaca mulatta) on their adult immune and endocrine responses were studied. Prior to the social challenge, the monkeys were reared either by their mother or in a peer group. Monkeys were treated with either a serotonergic agonist (fluoxetine), a noradrenergic agonist (desipramine), or saline during social separation. Non-separated, saline-treated monkeys served as control monkeys. In order to evaluate immune effects of early antidepressant treatment, adult monkeys were immunized with a novel antigen, tetanus toxoid. Blood samples were collected prior to and at 4-5-day intervals for 28 days after immunization. Plasma total immunoglobulins (IgG and IgM), complement levels (C3 and C4), tetanus antibody titers, and cortisol were assessed. Antibody levels were lowest in monkeys treated with antidepressants regardless of specific drug treatment or early rearing condition. Drug-treated subjects had elevated plasma immunoglobulins and complement protein levels. Cortisol was also highest in drug-treated subjects. These results should be considered when prescribing commonly used antidepressants for treatment of childhood disorders.
The selective serotonin uptake inhibitor (SSRI) fluoxetine has been shown to not only increase the extracellular concentrations of serotonin, but also dopamine and norepinephrine extracellular concentrations in rat prefrontal cortex. The effect of other SSRIs on monoamine concentrations in prefrontal cortex has not been thoroughly studied.
The aim of this study was to compare the ability of five systemically administered selective serotonin uptake inhibitors to increase acutely the extracellular concentrations of serotonin, norepinephrine and dopamine in rat prefrontal cortex.
The extracellular concentrations of monoamines were determined in the prefrontal cortex of conscious rats using the microdialysis technique.
Fluoxetine, citalopram, fluvoxamine, paroxetine and sertraline similarly increased the extracellular concentrations of serotonin from 2- to 4-fold above baseline. However, only fluoxetine produced robust and sustained increases in extracellular concentrations of norepinephrine and dopamine after acute systemic administration. Fluoxetine at the same dose blocked ex vivo binding to the serotonin transporter, but not the norepinephrine transporter, suggesting that the increase of catecholamines was not due to non-selective blockade of norepinephrine uptake. Prefrontal cortex extracellular concentrations of fluoxetine at the dose that increased extracellular monoamines were 242 nM, a concentration sufficient to block 5-HT(2C) receptors which is a potential mechanism for the fluoxetine-induced increase in catecholamines.
Amongst the SSRIs examined, only fluoxetine acutely increases extracellular concentrations of norepinephrine and dopamine as well as serotonin in prefrontal cortex, suggesting that fluoxetine is an atypical SSRI.
Studies of rodents suggest that extracellular fluid and cerebrospinal fluid (CSF) serotonin (5-HT) concentrations provide a better index of released 5-HT than the frequently obtained measure of CSF 5-hydroxyindoleacetic acid (5-HIAA). The measurement of cisternal CSF 5-HT levels in the monkey might offer a method of assessing the effects of agents and actions on central 5-HT functioning in primate brain.
To address methodological issues related to the determination of monkey cisternal CSF 5-HT and to examine the effects of a selective serotonin reuptake inhibitor (SSRI) on the measure.
Monkey CSF was obtained by cisternal puncture and 5-HT levels determined by high performance liquid chromatography, after screening for blood contamination.
When blood contamination was minimized, a mean (+/-SD) basal concentration of cisternal CSF 5-HT 87+/-36 pg/ml (n=13) was observed. Good longitudinal stability (variances of 16 and 20%) of CSF 5-HT was demonstrated in two monkeys sampled over a 3-month period. A two-fold increase in CSF 5-HT was seen in seven animals treated with the SSRI sertraline (20 mg/kg PO, mean treatment period of 12 days): pre- and post-drug 5-HT concentrations were 85+/-39 and 162+/-53 pg/ml (P=0.0007); in contrast, levels of 5-HIAA decreased from 40.0+/-5.7 to 20.4+/-2.2 ng/ml (P=0.0001).
The measurement of monkey cisternal CSF 5-HT appears to provide a useful index of central 5-HT release. Initial results tend to support a role for increased extracellular 5-HT in the mechanism of action of chronically administered SSRIs.
The objective of this study was to evaluate the pharmacokinetic profile of fluoxetine (FLX) and its major metabolite, norfluoxetine (NORFLX), in children and adolescent patients undergoing psychiatric treatment. Twenty-one pediatric subjects--10 children (6-12 years) and 11 adolescents (13-18 years)--were administered 20 mg FLX for 60 days, with sparse blood samples taken throughout the open-label study. Subjects contributed 168 plasma concentrations. Pharmacokinetic parameters were estimated using a mixed effects nonlinear model. Mean steady-state FLX and NORFLX of 127 ng/mL and 151 ng/mL, respectively, were achieved in children and adolescents after 4 weeks of treatment, with high between-patient variability. FLX was 2-fold higher and NORFLX was 1.7-fold higher in children relative to adolescents; however, when normalized to body weight, FLX and NORFLX were similar for both age groups. Age, body weight, body mass index, and body surface area, modeled independently as continuous variables, significantly improved the population pharmacokinetic model when evaluated as patient factors. Body weight was the covariate retained in the final model. In conclusion, children have 2-fold higher FLX and NORFLX relative to adolescents that appear to be related to indices of body size. The accumulation profile and steady-state concentrations in adolescents appear similar to those in adults.
The selective serotonin reuptake inhibitor fluoxetine consists of equal amounts of R and S stereoisomers. In this study, we investigated the pharmacologic properties of the stereoisomers using transporter and receptor binding assays and in vivo microdialysis in freely moving rats. Binding to the transporter confirmed selectivity of R- and S-fluoxetine for the 5-HT transporter versus the dopamine (DA) and norepinephrine (NE) human transporters. Receptor binding studies demonstrated significant affinity of R-fluoxetine, but not S-fluoxetine, for human 5-HT(2A) and 5-HT(2C) receptor subtypes. Functional GTPgammaS binding studies indicated that R-fluoxetine is an antagonist at 5-HT(2A) and 5-HT(2C) receptors. In microdialysis studies, acute R- and S-fluoxetine increased extracellular levels of 5-HT, DA, and NE in prefrontal cortex (PFC), but R-fluoxetine caused significantly greater increases of catecholamines. R-fluoxetine increased extracellular levels of 5-HT and NE in PFC, nucleus accumbens, and hypothalamus, whereas it increased dopamine in PFC and hypothalamus, but not in DA-rich nucleus accumbens and striatum, thus indicating a regionally selective effect. The unexpected increases of extracellular catecholamines by a selective 5-HT uptake inhibitor like R-fluoxetine may be due to its antagonism of 5-HT(2C) receptors.
It is clear that selective serotonin reuptake inhibitors (SSRIs) act powerfully to inhibit serotonin (5-hydroxytryptamine, 5-HT) uptake centrally and peripherally. However, there are a number of critical unanswered questions concerning the effects of the drugs in adults and children. The influence of age and duration of treatment on the extent of uptake inhibition and on the enhancement of central serotonergic functioning are unclear. In addition, the relationship of these factors and effects to the therapeutic and adverse effects of the SSRIs remain to be clarified. The general clinical utility of platelet 5-HT measurement is reviewed and studies assessing central and peripheral uptake blockade in infants and children and non-human primates are discussed. Recent investigations of central neurochemical effects of the SSRIs in primates assessed through measurement of 5-HT and related compounds in cisternal cerebrospinal fluid (CSF) of the rhesus monkey are presented. In summary, the studies described have found that: human fetal exposure to SSRIs has substantial effects on 5-HT transport in utero; exposure to SSRIs through breastmilk of mothers treated for postpartum depression usually has negligible effects on 5-HT uptake; prescribed SSRIs appear to exert similar effects on 5-HT transporter blockade in children and adults; and rapid and sustained increases are seen in monkey cisternal CSF levels of 5-HT upon initiation of SSRI administration. The implications of the observations in terms of behavioral effects, clinical practice, and underlying mechanisms of action of the SSRIs are discussed.
Fundamental questions remain regarding the actions of the selective serotonin reuptake inhibitors (SSRIs).
To examine the time course of central and peripheral neurochemical effects of sertraline (SER) in non-human primates.
SER (20 mg/kg, p.o.) or placebo were administered daily for 4 weeks to two groups of six young adult male rhesus monkeys. Both groups received placebo during a 3-week baseline lead-in period and for 6 weeks after discontinuation. Blood and cisternal cerebrospinal fluid (cCSF) samples were obtained on days -21, -14, -7, 0, +3, +7, +14, +21, +28, +35 and +70.
In animals receiving SER, mean (+/-SD) levels of cCSF serotonin (5-HT) increased from 38.6+/-9.0 pg/ml at baseline to 128+/-46.4 pg/ml during treatment (paired t=4.17, P=0.014). Concentrations of cCSF 5-HT were 290% of baseline on day 0 (+3 h), ranged from 260% to 436% of baseline during treatment, and returned to baseline 7 days after discontinuation. Levels of cCSF 5-hydroxyindoleacetic acid declined to 51+/-2.0% of baseline by day +3 and remained at similarly reduced levels during treatment. Plasma drug levels and decrements in platelet 5-HT were similar to those seen in patients.
SER rapidly and substantially increases cCSF levels of 5-HT in primates, the extent of elevation is relatively constant during prolonged administration, and values return to baseline shortly after discontinuation. The results suggest that response latency for SSRIs in depression is not due to gradually increasing brain extracellular fluid 5-HT levels and tend not to support theories that posit SSRI response latency as being due to autoreceptor desensitization, transporter downregulation, or drug accumulation.
Allelic variation of the monoamine oxidase A (MAOA) gene has been implicated in conduct disorder and antisocial, aggressive behavior in humans when associated with early adverse experiences. We tested the hypothesis that a repeat polymorphism in the rhesus macaque MAOA gene promoter region influences aggressive behavior in male subjects.
Forty-five unrelated male monkeys raised with or without their mothers were tested for competitive and social group aggression. Functional activity of the MAOA gene promoter polymorphism was determined and genotypes scored for assessing genetic and environmental influences on aggression.
Transcription of the MAOA gene in rhesus monkeys is modulated by an orthologous polymorphism (rhMAOA-LPR) in its upstream regulatory region. High- and low-activity alleles of the rhMAOA-LPR show a genotype x environment interaction effect on aggressive behavior, such that mother-reared male monkeys with the low-activity-associated allele had higher aggression scores.
These results suggest that the behavioral expression of allelic variation in MAOA activity is sensitive to social experiences early in development and that its functional outcome might depend on social context.
It is known that selective serotonin reuptake inhibitors, widely used as antidepressive drugs, act by inhibiting the cell reuptake of serotonin, but their effect on the catecholaminergic system is not yet completely understood. In this study, we investigated plasma concentrations of norepinephrine, epinephrine and dopamine after acute and chronic administration of fluoxetine in depressive patients. Twelve patients affected by major depression received a single oral dose of fluoxetine in the morning, 5 mg in the first 5 days, 10 mg from the 6th to the 10th day and 20 mg from the 11th to the 40th day. Twelve healthy subjects received a placebo under identical testing procedures. Blood samples were collected at baseline and 7, 10 and 24 h after drug administration on the 1st day of fluoxetine administration at a dose of 5 mg, and on the 1st and the 30th day of fluoxetine administration at a dose of 20 mg (days 11 and 40 of treatment, respectively). We found that plasma norepinephrine, epinephrine and dopamine levels significantly increased after acute and chronic treatment (p < 0.001), reaching the highest concentrations on the last day. No significant changes of these parameters were observed in control patients.
The effects of two serotonergic agents--fluoxetine, a serotonin (5-HT) reuptake inhibitor, and buspirone, a 5-HT 1a agonist--on rates of self-injurious and stereotypic behavior were examined in 15 adult male Macaca mulatta. All animals received a placebo for 2 weeks followed by either buspirone or fluoxetine for 12 weeks. Behavior was monitored using a focal sampling technique throughout the study and for 2 weeks post-study. Cerebrospinal fluid (CSF) samples and body weights were obtained pre-study, at the ends of placebo and treatment phases, and post-study. Fluoxetine and buspirone were significantly effective in reducing rates of self-biting during treatment weeks 1 to 8 and self-directed stereotypic behavior during weeks 5 to 12 and post-treatment. No significant effect of either treatment on hair-plucking, stereotypic pacing, saluting, or head tossing was identified. The duration of neutral behavior increased, and rates of scratching and yawning decreased in the buspirone-treated condition. In the fluoxetine-treated condition, rates of yawning, scratching, and self-directed grooming were higher overall compared with those of buspirone-treated animals, and rates of scratching increased significantly (P < 0.05) in weeks 9 to 12; these findings suggest that animals in the fluoxetine-treated condition experienced higher levels of anxiety throughout the study. In both treatment conditions, concentrations of CSF 5-HIAA (5-HT metabolite) were significantly lower (P < 0.05) than placebo concentrations. Fluoxetine and buspirone may be efficacious for treatment of self-injurious and self-directed stereotypic behavior in macaques. Further studies are required to determine the optimal dosages and treatment length.
Polymorphisms in the serotonin transporter gene (5-HTT) may influence antidepressant response to selective serotonin reuptake inhibitors (SSRIs). The norepinephrine transporter (NET) is the analogous target for norepinephrine reuptake inhibitors (NRIs).
To determine whether antidepressant responses to SSRIs or NRIs are associated with genetic polymorphisms of the corresponding monoamine transporters.
A 6-week naturalistic treatment study with blinded outcome evaluation of 241 Korean inpatients and outpatients with major depression at an academic psychiatry service. Patients were recruited to the study from March 1998 through February 2003.
Treatment with an SSRI (fluoxetine or sertraline; n = 136) or an NRI (nortriptyline; n = 105) antidepressant. Adherence was assessed by measuring plasma concentration at 4 weeks. Patients were genotyped for s/l polymorphisms in 5-HTT promoter region (5-HTTLPR), 5-HTT intron 2 s/l variation, and NET G1287A variation of exon 9.
An SSRI and NRI response (defined as > or =50% decrease in Hamilton Rating Scale for Depression score at 6 weeks).
NRI response was associated with the NET G1287A polymorphism (odds ratio [OR], 7.54; 95% confidence interval [CI], 2.53-22.49; P<.001). An SSRI response was associated with the 5-HTT intron 2 s/l variation (OR, 20.11; 95% CI, 4.27-94.74; P<.001). The 5-HTTLPR was also associated with an SSRI response (OR, 3.34; 95% CI, 1.41-7.91; P = .006). In contrast to studies in white patients, the favorable allele for SSRI response was S 5-HTTLPR. The S 5-HTTLPR was associated also with NRI response (OR, 3.73; 95% CI, 1.32-10.53; P = .01). The NET polymorphism was not associated with an SSRI response. The NET G1287A GG genotype (56% of the population) was associated with better response to the NRI (83.3% [35/42]) than to SSRI (58.7% [44/75]) (OR, 3.52; 95% CI, 1.39-8.95; P = .006). Some genotype combinations were associated with high rates of antidepressant response and others with low rates of response.
Monoamine transporter gene polymorphisms were associated with response to antidepressants with homologous monoamine transporter targets. Combinations of polymorphisms were informative for response and nonresponse. Confirmation of these preliminary findings would permit refined pharmacogenetic selection of antidepressant treatment.
Recent studies have shown that selective serotonin reuptake inhibitors (SSRIs) such as fluoxetine are accumulated in the tissues of fish as a result of discharges of pharmaceuticals into surface waters from municipal wastewater treatment plants. In this study, an analytical method based on liquid chromatography with atmospheric pressure chemical ionization and tandem mass spectrometry (LC-APCI-MS/MS) was developed and validated for the determination of residues of paroxetine, fluoxetine and its active metabolite, norfluoxetine, in fish tissue. The procedure for sample preparation includes extraction of tissue by pressurized liquid extraction (PLE), followed by cleanup on a mixed-mode solid phase extraction (SPE) cartridge, Oasis MCX. With the optimized method, matrix interferences were reduced and recoveries >85% were obtained. The limits of quantitation (LOQ) determined by analysis of spiked fish tissue were 0.24, 0.07, and 0.14 ng/g wet weight for paroxetine, fluoxetine and norfluoxetine, respectively. This method was successfully applied to the analysis of samples of fish collected from Hamilton Harbour in Ontario, Canada, which is an urbanized and industrialized embayment of Lake Ontario. These analyses showed that the three analytes were present in fish tissues at concentrations up to approximately 1 microg/kg wet weight.
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Approval letter: application number 18-936/SE5-064. Center for Drug Evaluation and Research, Food and Drug Administration Fontenot MB The effects of fluoxetine and buspirone on selfinjurious and stereotypic behavior in adult male rhesus macaques
FDA (2003) Approval letter: application number 18-936/SE5-064.
Center for Drug Evaluation and Research, Food and Drug
Administration
Fontenot MB, Padgett EE 3rd, Dupuy AM, Lynch CR, De Petrillo PB,
Higley JD (2005) The effects of fluoxetine and buspirone on selfinjurious and stereotypic behavior in adult male rhesus macaques.
Comp Med 55:67–74