Solagé is a combination product composed of 2% mequinol (4-hydroxyanisole) and 0.01% tretinoin (all-trans-retinoic acid) in an ethanolic solution, which is being studied for its safety and efficacy as a topical treatment for disorders of skin hyperpigmentation. The purpose of this study was to evaluate the extent of percutaneous absorption of [3H]tretinoin and to estimate the systemic exposure to mequinol from this combination product when topically applied to the backs of healthy subjects. Eight subjects received bid topical applications of nonradiolabelled 2% mequinol/0.01% tretinoin solution on a 400 cm2 area of the back for 14 days. The subjects then received a single topical application of 2% mequinol/0.01% [3H]tretinoin solution. After 12 h, the radiolabelled dose was removed and bid treatment with nonradiolabelled 2% mequinol/0.01% tretinoin solution was continued for 7 days. Plasma, urine and faecal samples were analysed for total radioactivity and plasma was analysed for both mequinol and tretinoin by GC/MS procedure. Mean percutaneous absorption of [3H]tretinoin based on the cumulative recoveries of radioactivity in the urine and faeces was about 4.5% (median 2.18%). Tretinoin concentrations in plasma did not increase above endogenous levels. This was consistent with the concentrations of radioactivity in plasma, which showed an average Cmax of 91 pg-eq/mL (median 26 ng/mL). Average Cmax and AUC(0-12 h) values for mequinol were 10 ng/mL and 33 ng h/mL, respectively. Based on the results of this study, systemic toxicity from topical application of tretinoin in this formulation is unlikely, because percutaneous absorption of tretinoin is minimal and because endogenous levels of tretinoin are not increased following bid dosing with this combination formulation. The safety of mequinol in this combination formulation is supported by the low systemic exposures of the subjects in this study compared with the systemic exposures at the highest doses in the dermal toxicity studies in mice (16.6-fold) and rats (34.6-fold).
After intravenous administration of AS 2-006A, 20, 50, and 90 mg/kg, to rats, the pharmacokinetic parameters, terminal half-life (69.8-86. 6 min), mean residence time (56.2-75.2 min), apparent volume of distribution at steady state (809-1040 mL/kg), and total body clearance (11.4-11.9 mL/min/kg), were dose-independent. After topical application of 0.5 or 1% AS 2-006A ointment, 300 mg, to abraded rat skin, the absorbed amounts were dose (0.5 and 1%) and time (30, 60, 120, 240, 360 and 480 min)-independent; the value was approximately 20%. The tissue-to-plasma ratios of AS 2-006A were greater than unity in all rat tissues studied, except in the muscle and large intestine. AS 2-006A was stable for up to 24 h incubation in rat plasma, and human plasma and urine; however, it seemed not to be stable in rat urine; the disappearance rate constant was 0.0218/h. AS 2-006A reached equilibrium fast between plasma and blood cells, and the equilibrium plasma/blood cells partition ratios were independent of the initial rabbit blood concentrations of AS 2-006A, 10, 20, and 50 microg/mL; the mean values were in the range of 2.38-2.75 for three rabbit blood. The protein binding of AS 2-006A to rat plasma was high, as the drug was under detection limit in the filtrate at the plasma concentrations of the drug, ranging from 7.21 to 228 microg/mL.
Nemifitide (4-fluoro-L-phenylalanyl-trans-4-hydroxy-L-prolyl-L-arginylglycyl-L-tryptophanamide ditrifluoroacetate) is a novel antidepressant, currently in phase 2/3 clinical trials. The purpose of our phase 1 clinical trials (conducted over a three year period) was to provide safety and pharmacokinetic data to support its clinical development as an antidepressant drug. Single and multiple doses ranging from 18 to 320 mg were administered subcutaneously to healthy volunteers in five phase 1 studies. Plasma concentrations of unchanged parent drug were determined by a validated LC/MS/MS method in blood samples collected at timepoints between 10 min and 72 h after dosing. Nemifitide was rapidly absorbed (C(max) at 10 min) and eliminated (t(1/2) 15-30 min) in most subjects. Regression and power model analyses were used to evaluate the data. The results indicate that pharmacokinetic parameters: AUC(0-t), AUC (0-infinity) and C(max), were close to dose proportional in the dose range investigated. There was no evidence of systemic accumulation of drug following 5 daily doses. No serious adverse events or clinically significant systemic adverse events occurred at any of the doses investigated in the over 100 subjects dosed in these studies. Drug-related adverse events were limited to local and transient skin reactions (pain and/or erythema) at the injection site, especially at the high doses administered: 240 and 320 mg.
The mechanism of the nonlinear pharmacokinetics of TAK-044 in rats was shown from in vivo and in vitro studies to be due to capacity-limited hepatic uptake. In the rats, which were given intravenous injections of (14)C-labeled TAK-044 ([(14)C]TAK-044) (1, 3, 10, 30 and 100 mg/kg), the AUC(inf) per unit dose of unchanged compound increased remarkably. An analysis model indicated that the CL(tot), V(1) and k(12) values of TAK-044 decreased significantly with increasing dose, whereas the k(el) values remained constant over the doses examined. The uptake clearance of [(14)C]TAK-044 by several tissues was investigated by an integration plot at doses from 0.3 to 60 mg/kg. This study showed that the liver played the principal role in the removal of TAK-044 from the plasma, while hepatic uptake was capacity-limited at doses greater than 30 mg/kg. The hepatic uptake study using rat hepatocytes indicated that a carrier-mediated transport system contributed to the hepatic uptake of TAK-044, and this system had high affinity (K(m,in vitro); 8.4 micromol/L) with low capacity (V(max,in vitro); 86.3 pmol/mg protein/min). These results show that the saturation of hepatic uptake by the carrier-mediated transport system could explain the nonlinear pharmacokinetics of TAK-044 in rats.
A study was conducted to (i) characterize the multiple-dose pharmacokinetics of oral montelukast sodium (MK-0476), 10 mg d-1 in healthy young subjects (N = 12), (ii) evaluate the pharmacokinetics of montelukast in healthy elderly subjects (N = 12), and (iii) compare the pharmacokinetics and oral bioavailability of montelukast between elderly and young subjects. Following oral administration of montelukast sodium, 10 mg d-1 (the therapeutic regimen for montelukast sodium) for 7 d, there was little difference in the plasma concentration-time profiles of montelukast in young subjects between day 1 and day 7 dosing. On average, trough plasma concentrations of montelukast were nearly constant, ranging from 18 to 24 ng mL-1 on days 3-7, indicating that the steady state of montelukast was attained on day 2. The mean accumulation ratio was 1.14, indicating that this dose regimen results in a 14% accumulation of montelukast. In elderly subjects, mean values of plasma clearance (Cl), steady-state volume of distribution (Vss), plasma terminal half-life (t1/2), and mean residence time in the body (MRTIV) following a 7 mg intravenous (5 min infusion) administration of montelukast sodium in the elderly were 30.8 mL min-1, 9.7 L, 6.7 h, and 5.4 h, respectively. Following a 10 mg oral dose, the bioavailability of montelukast in healthy elderly averaged 61%, very close to that (62%) determined previously in healthy young subjects. Also following the 10 mg oral administration, the mean values of AUC0-->infinity, Cmax, tmax, and t1/2, and the mean plasma concentration-time profile of montelukast in the elderly, were generally similar to those in young subjects, indicating that age has little or no effect on the pharmacokinetics of montelukast. There is no need to modify dosage as a function of age.
AHN 1-055, a benztropine (BZT) analog, binds with high affinity to the dopamine transporter (DAT), possesses behavioral, pharmacokinetic (PK) and brain microdialysate dopamine (DA) profiles distinct from cocaine. Accordingly, the objectives of this study were to evaluate the pharmacokinetics and dopamine release of AHN 1-055, in the presence of cocaine.
Male Sprague Dawley rats ( approximately 300 g) were administered 5 mg/kg of AHN 1-055 and cocaine i.v. and blood and brain samples were collected over 36 h. In addition, dialysis probes were stereotaxically implanted into the nucleus accumbens and extracellular fluid (ECF) DA levels were measured. PK and PD models were used to describe the relationship between the AHN 1-055, cocaine and DA levels.
No significant (p< 0.05) differences were found in the PK parameters of AHN 1-055 alone (V(dss) = 18.7 l/kg, Cl = 1.8 l/h/kg and t(1/2) = 7.69 h) or AHN 1-055 with cocaine (V(dss)=17.4 l/kg, Cl = 1.9 l/h/kg and t(1/2) = 6.82 h). The brain-to-plasma (B/P) ratios (B/P(AHN 1-055) = 4.8 vs B/P(with cocaine) = 4.4) and half-lives (t(1/2(AHN 1-055)) = 6.2 h vs t(1/2(cocaine) = )5.6 h for AHN 1-055 alone and with cocaine were comparable. AHN 1-055 DA profiles were significantly different after co-administration with cocaine. There were no differences in the IC(50) for AHN 1-055, with cocaine, however, the IC(50) for cocaine was significantly reduced with AHN 1-055.
The PK parameters of AHN 1-055 were not changed, however, the effect on DA levels was affected when cocaine was administered with AHNDA profile is affected when dosed with cocaine. This latter effect is a desirable attribute in the development of a medication as a potential substitute therapeutic medication for the treatment of cocaine abuse.
To determine the effect of gender on the pharmacokinetics of eslicarbazepine acetate, a novel voltage-gated sodium channel blocker in the development for the treatment of epilepsy and bipolar disorder.
Single-centre, open-label, parallel-group study in 12 female and 12 male healthy subjects. The study consisted of a single-dose (600 mg) period and a multiple-dose (600 mg, once-daily, for 8 days) period, separated by 4 days.
Eslicarbazepine acetate was rapidly and extensively metabolized to eslicarbazepine (S-licarbazepine), the main active metabolite. Following a single-dose, arithmetic mean eslicarbazepine maximum plasma concentrations (C(max)) and area under the plasma concentration-time curve over 24 h (AUC(0-24)) and from 0 to infinity (AUC(0-infinity)) were, respectively, 9.3 microg/ml, 128.5 microg h/ml and 171.9 microg h/ml in male subjects and 10.1 microg/ml, 150.1 microg h/ml and 205.0 microg h/ml in female subjects. At steady-state, C(max), AUC(0-24) and AUC(0-infinity) were 15.5 microg/ml, 207.8 microg h/ml and 295.8 microg h/ml in male subjects, and 16.8 microg/ml, 214.5 microg h/ml and 295.2 microg h/ml in female subjects. Steady-state plasma concentrations were attained at 4 to 5 days of administration in both groups. Eslicarbazepine C(max), AUC(0-24) and AUC(0-infinity) female:male geometric mean ratios (90%CI) were, respectively, 1.09 (0.94; 1.24), 1.16 (1.00; 1.33) and 1.17 (0.99; 1.38) following single-dose, and 1.10 (0.97; 1.25), 1.04 (0.92; 1.17) and 1.01 (0.88; 1.16) at steady-state.
At steady-state, the pharmacokinetic profile of eslicarbazepine acetate was not affected by gender.
1,2- and 1,3-glyceryl dinitrates (1,2-GDN and 1,3-GDN) are the primary metabolites of glyceryl trinitrate, a commonly used anti-anginal agent. The goal of this study was to examine the pharmacokinetic properties of these metabolites in rats. Sprague-Dawley rats were infused intravenously with 0.25 or 2.0 micrograms min-1 of either 1,2- or 1,3-GDN for 70 min, during which steady state blood concentrations were achieved. Post-infusion blood samples were collected for 30 min. 1,2-GDN was found to possess slightly higher clearance (32.3 vs 20.8 ml min-1 kg-1) and volume of distribution (695 vs 454 ml kg-1) than 1,3-GDN; however, the two metabolites exhibited similar mean residence times (22.0 vs 21.8 min). Upon an 8-fold increase in the infusion rate, the pharmacokinetic parameters were not significantly altered for either 1,2- or 1,3-GDN. When each GDN was co-infused with an 8-fold higher dose of the other GDN, there were also no significant changes in the parameters.
The disposition of 6-(4-(2,5÷fluorophenyl)oxazol-5-yl)- 3-isopropyl-[1,2,4]-triazolo[4,3-a]pyridine (1), a potent and selective inhibitor of mitogen activated protein (MAP) kinase p38α, was characterized in several animal species in support of its selection for preclinical safety studies and potential clinical development. 1 demonstrated generally favorable pharmacokinetic properties in all species examined. Following intravenous (i.v.) administration, 1 exhibited low volumes of distribution at steady state (Vdss) ranging from 0.4-1.3 l/kg (2.4-26 l/m2) in the rat, dog and monkey. Systemic plasma clearance was low in cynomolgus monkeys (6.00 ml/min/kg, 72.0ml/min/m2) and Sprague-Dawley rats (7.65 ± 1.08ml/min/ kg, 45.9 ± 6.48 ml/min/m2 in male rats and 3.15 ± 0.27 ml/min/kg, 18.9 ± 1.62 ml/min/m2 in female rats) and moderate in beagle dogs (12.3 ± 5.1 ml/min/kg, 246 ± 102 ml/min/m2) resulting in plasma half-lives ranging from 1 to 5h in preclinical species. Moderate to high bioavailability of 1 was obsernkey and human. 1 as well as the active metabolite 2 did not exhibit competitive inhibition of the five major cytochrome P450 enzymes namely CYP1A2, 2C9, 2C19, 2D6 and 3A4 (IC50>50 μM). Overall, these results indicate that the absorption, distribution, metabolism and excretion (ADME) profile of 1 is relatively consistent across preclinical species and predict potentially favorable pharmacokinetic properties in humans, supporting its selection for toxicity/safety assessment studies and possible investigations in humans as an anti-inflammatory agent.
Previous studies have shown that 1α,25-dihydroxyvitamin D3 [1,25(OH)2 D3 ] treatment in mice resulted in induction of intestinal and renal Cyp24a1, increased hepatic Cyp7a1 expression and activity, and increased renal Mdr1/P-gp and intestinal and renal Trpv6 expression. The present study compared the equimolar efficacies of 1α-hydroxyvitamin D3 [1α(OH)D3 ] (6 nmol/kg i.p. q2d x4), a lipophilic precursor with a longer plasma half-life that is converted to 1,25(OH)2 D3 , on VDR target genes. To clarify whether changes in VDR genes was due to VDR and not secondary, FXR-directed effects, exemplified by changes in Cyp7a1 in rat liver due to increased bile acid absorption, wildtype [fxr(+/+)] and FXR knockout [fxr(-/-)] mice were used to distinguish between VDR and FXR effects. With the exception of hepatic Sult2a1 mRNA that was increased equally well by 1α(OH)D3 and 1,25(OH)2 D3 , 1α(OH)D3 treatment led to higher increases in hepatic Cyp7a1, renal Cyp24a1, VDR, Mdr1, and Mrp4, and intestinal Cyp24a1 and Trpv6 mRNA expression in both fxr(+/+) and fxr(-/-) mice when compared to those of 1,25(OH)2 D3 treatment. A similar induction in protein expression and microsomal activity of hepatic Cyp7a1 and renal P-gp and Mrp4 protein expression was observed for both compounds. A higher intestinal induction of Trpv6 resulted in greater hypercalcemic effect, following 1α(OH)D3 treatment. The higher activity of 1α(OH)D3 was explained by its rapid conversion to 1,25(OH)2 D3 in tissue sites, furnishing higher plasma and tissue 1,25(OH)2 D3 levels compared to those from 1,25(OH)2 D3 -treated mice. In conclusion, 1α(OH)D3 exerts a greater efficacy of VDR gene induction than equimolar doses of 1,25(OH)2 D3 in mice. This article is protected by copyright. All rights reserved.
It has been reported that the expressions of hepatic microsomal cytochrome P450 (CYP) 1A1/2, 2B1/2 and 3A1/2 were not changed in rats with water deprivation for 72 h (rat model of dehydration) compared with the controls. It has been also reported that 1,3-dimethyluric acid (1,3-DMU) was formed from theophylline via CYP1A1/2 in rats. Hence, it could be expected that the formation of 1,3-DMU could be comparable between the two groups of rats. As expected, after both intravenous and oral administration of theophylline at a dose of 5 mg/kg to the rat model of dehydration, the AUC of 1,3-DMU was comparable to the controls. After both intravenous and oral administration of theophylline to the rat model of dehydration, the Cl(r) of both theophylline and 1,3-DMU was significantly slower than the controls. This could be due to significantly smaller urinary excretions of both theophylline and 1,3-DMU since the AUC of both theophylline and 1,3-DMU were comparable between the two groups of rats. The smaller urinary excretion of both theophylline and 1,3-DMU could be due to urine flow rate-dependent timed-interval renal clearance of both theophylline and 1,3-DMU in rats.
We tested the hypothesis that the small intestine is capable of the first-pass, reductive metabolism of xenobiotics. A simplified version of the isolated vascularly perfused rat small intestine was developed to test this hypothesis with 1,3-dinitrobenzene (1,3-DNB) as a model xenobiotic. Both 3-nitroaniline (3-NA) and 3-nitroacetanilide (3-NAA) were formed and absorbed following intralumenal doses of 1,3-DNB (1.8 or 4.2 mumol) to isolated vascularly perfused rat small intestine. Dose, fasting, or antibiotic pretreatment had no effect on the absorption and metabolism of 1,3-DNB in this model system. The failure of antibiotic pretreatment to alter the metabolism of 1,3-DNA indicated that 1,3-DNB metabolism was mammalian rather than microfloral in origin. All data from experiments initiated with lumenal 1,3-DNB were fit to a pharmacokinetic model (model A). ANOVA analysis revealed that dose, fasting, or antibiotic pretreatment had no statistically significant effect on the model-dependent parameters. 3-NA (1.5 mumol) was administered to the lumen of isolated vascularly perfused rat small intestine to evaluate model A predictions for the absorption and metabolism of this metabolite. All data from experiments initiated with 3-NA were fit to a pharmacokinetic model (model B). Comparison of corresponding model-dependent pharmacokinetic parameters (i.e. those parameters which describe the same processes in models A and B) revealed quantitative differences. Evidence for significant quantitative differences in the pharmacokinetics or metabolism of formed versus preformed 3-NA in rat small intestine may require better definition of the rate constants used to describe tissue and lumenal processes or identification and incorporation of the remaining unidentified metabolites into the models.
1954U89, 1,3-diamino-7-(1-ethylpropyl)-8-methyl-7H-pyrrolo-(3, 2-f)quinazoline, is a potent, lipid-soluble inhibitor of dihydrofolate reductase. The pharmacokinetics and bioavailability of 1954U89 were examined in male beagle dogs and male CD rats. Dogs received single intravenous (2.5 mg kg-1) and oral (5.0 mg kg-1) doses of 1954U89 with and without successive administration of calcium leucovorin. Single intravenous (5.0 mg kg-1) and oral (10 mg kg-1) doses of [1,3-14C2]1954U89 were administered to rats. Plasma concentrations of total radiocarbon were determined by scintillation counting, and intact 1954U89 was measured by HPLC. The mean plasma half-life was 3.2 +/- 0.62 and 4.2 +/- 0.68 h after intravenous and oral administration, respectively, to dogs. The pooled plasma half-life after intravenous administration to rats averaged 1.2 h; a reliable plasma half-life value after oral administration could not be determined. Mean total-body clearance was 2.4 +/- 0.39 and 4.5 +/- 1.1 L h-1 kg-1 after intravenous and oral administration, respectively, to dogs, and averaged 12 and 77 L h-1 kg-1 after intravenous and oral administration, respectively, to rats. Neither clearance nor bioavailability of 1954U89 in dogs was affected significantly by administration of calcium leucovorin. Absolute bioavailability was 54 +/- 12% in dogs and 16% in rats.
In man, 14C-2-ylcyanamide-1 3 4-thiadiazole (LY217896) accumulates into red blood cells (RBCs) where it is rapidly metabolized. Both in man and ex vivo, within a few hours of administration of 14C-LY217896 at least two intracellular metabolites were detected within the RBCs using HPLC. These metabolites were never detected extracellularly. After 24 h no detectable radioactivity was found in the plasma and all the radioactivity was detected within the cellular fraction. All radioactivity was identified as a single peak within the RBCs, indicating the metabolite(s) to be highly polar compared to LY217896. Parent LY217896 was never detected within the RBCs at any time point, suggesting transport, either by diffusion or a carrier mediated mechanism, was the rate limiting step. Due to the nature of the preparation it was impossible to separately characterize uptake and biotransformation. Nevertheless, uptake/biotransformation was found to be temperature sensitive, sodium independent, and energy dependent. Both niacin and vitamin B6, but not nicotinamide, competitively blocked the uptake and subsequent intracellular metabolism of LY217896.
The metabolism of SCH 40120, which is the clinically effective antipsoriatic drug 10-(3-chlorophenyl)-6,8,9,10-tetrahydrobenzol[b][1,8]naphthyrid in-5(7H)-one, was determined in vitro. Rat, dog, cynomolgus monkey, and human liver slices hydroxylated the aliphatic, cyclohexenyl ring of the drug and conjugated the resulting carbinol. The identified metabolites comprised the corresponding 6-, 7-, and 9-carbinols, the glucuronide of the 6-carbinol, and the 6-ketone derived from the parent drug. Although the three carbinols appeared in the liver isolates of all species studied, the relative amounts of these metabolites varied across species. With a high, non-physiological ratio of substrate to liver, the 6-carbinol and its glucuronide were the major metabolites in human and monkey, whereas the 6-ketone was a minor metabolite in dog. Containing a stereogenic axis and center, the 6-carbinol existed as diastereomeric atropisomers. Its structure was established by 13C and 1H NMR spectroscopy, mass spectrometry, and comparison to an authentic sample.
The pharmacokinetics of cefadroxil and cephalexin were examined following single oral doses of either 250, 500 or 1000 mg to a total of 36 healthy volunteers. The volunteers were divided into groups of 12 per dose-group and solution doses of cefadroxil or cephalexin were administered after an overnight fast according to a crossover design for the cephalosporins but not for doses. Serial blood and urine samples were collected from each individual and were analyzed for cefadroxil or cephalexin using validated HPLC assays with UV detection. The individual subject plasma concentration-time data for each cephalosporin were analyzed using noncompartmental methods. Profiles for cephalexin in plasma showed sharper and higher peaks than those for cefadroxil. Although values for the peak concentrations (Cmax) for cefadroxil were lower than that of cephalexin, the levels of cefadroxil in plasma and urine remained above the reported minimum inhibitory concentrations of susceptible organisms for longer period of time than those of cefalexin. The elimination half-life (t1/2) of cefadroxil (about 2 h) was significantly longer than that of cephalexin (about 1 h). The values for Cmax and AUC0-infinity values for both these cephalosporins showed dose-proportional increase, whereas t1/2, renal clearance (CLR) remained independent of dose. These observations confirm that cefadroxil and cephalexin obey linear pharmacokinetics. The CLr of both the cephalosporins were significantly higher than the average glomerular filtration rate at each dose level. The urinary recovery (% Xu) of each cephalosporin, accounted for over 80 per cent of the administered dose, and no significant differences in % Xu were observed between the two cephalosporins. These data suggest that the systemic availability of cefadroxil and cephalexin is similar at each dose level.
The pharmacokinetics and dose-exposure relationship of an extended-release formulation of metformin (ER-metformin) was investigated in a randomized, single-dose, four-period crossover study in 24 healthy male volunteers. During each study period, subjects received a randomly assigned dose containing 1000, 1500, 2000 or 2500 mg metformin. Blood samples were drawn 0-72 h after dosing for pharmacokinetic and dose-proportionality assessment. Although several pairwise comparisons between dose groups were significant (p<0.05) with respect to dose-normalized C(max), AUC(0-72 h), and AUC( infinity ), the magnitude of the difference across the dose range was <20% for AUC(0-72 h) and AUC( infinity ), and was < or = 30% for C(max). The results indicate a consistent and predictable increase in metformin exposure with an extended-release formulation of metformin over 1000 to 2500 mg.
Eight healthy male, Vietnamese subjects were administered 1 x 250, 2 x 250, and 4 x 250 mg artemisinin capsules in a cross-over design with randomized sequence with a 7-day washout period between administrations. The inter-individual variability in artemisinin pharmacokinetics was large with parameter coefficient of variation (CV) typically between 50-70%. The parameter with the smallest variability was the elimination half-life (CV approximately equal to 30-40%). Analysis of variance indicated also a large intra-subject variability. (CV, or = 24%) for the dose-normalized area under the plasma concentration-time curve (AUC/dose). The pharmacokinetic results suggested artemisinin to be subject to high pre-systemic extraction. Artemisinin half-life could not predict the extent of in vivo exposure to the drug, there being no correlation between half-life and oral clearance. Artemisinin oral plasma clearance was about 400 L h-1 exhibiting a slight decrease with dose, although the effect was weak. Thus results from studies using different artemisinin doses may, within the studied dose range, be compared without the complication of disproportionate changes in drug exposure with varying dose levels. Half-lives appeared to increase with dose. An observed period effect in the analysis of variance was tentatively associated with time-dependency in artemisinin pharmacokinetics. There was a high correlation between artemisinin plasma concentrations determined at various time-points after drug administration and the AUCs after the 500 and 1000 mg doses, but less so after the 250 mg dose. This may show a tentative approach to assess the systemic exposure of the patients to artemisinin from the determination of artemisinin plasma concentrations in one or two plasma samples only. Artemisinin was well tolerated with no apparent dose or time dependent effects on blood pressure, heart rate or body temperature.
A randomized, two-way, crossover, bioequivalence study in 24 fasting, healthy, male volunteers was conducted to compare two brands of aceclofenac 100 mg tablets, Aceclofar (Julphar, UAE) as test and Bristaflam (Bristol Myers Squibb, Egypt) as the reference product. The drug was administered with 240 ml of water after a 10 h overnight fast on two treatment days separated by 1 week washout period. After dosing, serial blood samples were collected for a period of 24 h. Plasma harvested from blood was analysed for aceclofenac by a validated HPLC method with UV-visible detection capable of detecting aceclofenac in the range 0.2-8.0 microg/ml with the limit of quantitation as 0.2 microg/ml. Various pharmacokinetic parameters including AUC(0-t), AUC(0- infinity ), C(max), T(max), T(1/2), and lambda(Z) were determined from plasma concentrations for both formulations and found to be in good agreement with reported values. AUC(0-t), AUC(0- infinity), and C(max) were tested for bioequivalence after log-transformation of data. No significant difference was found based on ANOVA; 90% confidence interval (100.0%-106.4% for AUC(0-t), 100.2%-106.8% for AUC(0- infinity ); 83.3%-102.8% for C(max)) of test/reference ratio for these parameters were found to be within the bioequivalence acceptance range of 80%-125%. Based on these statistical inferences, it was concluded that Aceclofar is bioequivalent to Bristaflam.
The disposition of 4-amino-5-chloro-2-[2-(methylsulfinyl)ethoxy]-N- [2-(diethylamino)ethyl] benzamide hydrochloride (ML-1035) following intravenous (10 mg kg-1) and oral (200 mg kg-1) dosing was investigated in male and female New Zealand white rabbits. After intravenous dosing ML-1035 was eliminated with a half-life of 1.45 +/- 0.49 h in males and 0.79 +/- 0.08 h in females. Volume of distribution at steady-state was 2.08 +/- 0.98 l kg-1 in males and 9.11 +/- 5.86 l kg-1 in females. Clearance averaged 2.99 +/- 1.11 l h-1 kg-1 in males and 16.73 +/- 7.29 l h-1 kg-1 in females. All pharmacokinetic parameters were significantly different between males and females (p < 0.05). Absolute bioavailability after oral administration was 7.35 per cent for males and 12.31 per cent for females, suggesting that ML-1035 undergoes significant first-pass elimination. Plasma area under the curve for the metabolites of ML-1035 after both oral and intravenous administration were also different between the two sexes. These data suggest that the disposition of ML-1035 shows significant differences between male and female rabbits.
Two investigations aimed to define the pharmacokinetic profile of a modified-release preparation of zaleplon (SKP-1041).
Protocol SOM001 was a 5-way crossover, double-blind, randomized trial comparing three novel modified-release formulations of zaleplon 15 mg (SKP-1041A, SKP-1041B, SKP-1041C) to placebo and immediate-release zaleplon 10 mg. Protocol SOM002 was a randomized, crossover, open-label trial to compare the pharmacokinetics of SKP-1041B after day and night administration. In SOM001, study drug was administered at 9:00 a.m. (fasted); blood samples were obtained beginning 1 h predose through 12 h postdose. In study SOM002, study drug was administered at 9:00 a.m. or 10:30 p.m.; blood samples were obtained beginning 1 h predose through 12 h postdose. Subjects were 19 (SOM001) and 23 (SOM002) healthy adults between ages 20-46.
Dose-normalized total AUCs for modified-release preparations A, B, C and immediate-release zaleplon were not significantly different; peak plasma concentrations were similar for A and B, and both were significantly higher than C. Time to peak plasma concentration for A, B, and C were 4-5 h compared to 1.5 h for immediate-release zaleplon; mean terminal phase half-life was in the range 1-2 h for A, B and immediate-release zaleplon. No significant differences were noted between day and night administration in the SOM002 study.
Zaleplon, 15 mg, in a novel, modified-release formulation (SKP-1041) had a time to peak plasma concentrations at 4-5 h postdose compared to 1.5 h for immediate-release zaleplon, 10 mg. The pharmacokinetic profile suggests this formulation may be useful for treating middle-of-the-night awakening.
A circulating in situ rat small intestine absorption model was used to study the lumenal metabolism and absorption of [14C]WR-1065. WR-1065 was found to be more tissue reactive and toxic than its phosphorylated form, ethiofos, at equimolar perfusate concentrations. The disappearance profiles of the radiolabeled drug and free WR-1065 indicate that WR-1065 is extensively metabolized in the intestinal lumen prior to absorption. Coadministration of disodium ethylenediaminetetraacetic acid enhances the absorption of the free thiol although not to the same extent as seen with ethiofos. Perfusion of WR-1065 in citrate buffer decreased lumenal degradation of the drug but resulted in decreased absorption. The total material converted to WR-1065 portal blood profiles following ethiofos and WR-1065 perfusion were altered possibly due to distribution and metabolism differences. This study coupled with earlier work completed on ethiofos have increased our understanding of the significant barriers to absorption observed following oral administration of these compounds.
Amifostine is a prodrug in which selectivity is largely determined by the preferential formation and uptake of its cytoprotective metabolite, WR-1065, in normal tissues as a result of differences in membrane-bound alkaline phosphatase activity. It was hypothesized that amifostine may be a good candidate for regional drug delivery to the liver because of its large hepatic extraction and total body clearance.
Rat livers were implanted with Walker-256 tumors. The tumor-bearing rats received 15 min infusions of amifostine (200 mg/kg) via the portal vein or the femoral vein. WR-1065 concentrations in the blood, liver and tumor were measured at various times.
The WR-1065 tumor portal dosing AUC15-60 was 40% of systemic dosing, and tumor concentrations following portal dosing were one-fifth of that following systemic dosing. The portal dosing WR-1065 liver AUC15-60 was 60% higher than the values for systemic dosing. The liver/tumor concentration ratios of WR-1065 following portal dosing were up to 8-fold higher than the ratio following systemic administration. Unfortunately, systemic exposure to WR-1065 was greater following portal vs systemic amifostine.
Amifostine may provide increased liver protection and decreased tumor protection from radio- or chemotherapy when administered by the portal vein. However, portal dosing also increases systemic exposure to WR-1065, which is associated with hypotension.
PLD-118 is a novel, oral antifungal drug, under development for the treatment of Candida infections. Possible metabolism of PLD-118 by rat, dog and human S9 liver homogenates and inhibition of human cytochrome P450 (CYP) enzymes were investigated. PLD-118 (10 and 100 microM) incubated for 0-60 min with S9 fractions and NADPH was determined by HPLC, using the Waters AccQ.Tag method after derivatization of amino acids to stable, fluorescent derivatives. CYP assays were performed using pooled human liver microsomes with substrates, selective towards human CYP1A2, CYP2A6, CYP2B6, CYP2C9, CYP2C19, CYP2D6, CYP2E1 and CYP3A, incubated at concentrations around the Km. Incubation mixtures were preincubated with PLD-118 (0.1-100 microM) or control inhibitor for 5 min. No metabolism of PLD-118 was detected with rat and dog S9 fractions. A small (8%) decrease in PLD-118 at 100 microM (not detected at 10 microM) with human microsomes was considered to be biologically irrelevant. PLD-118 did not inhibit any of the tested CYPs. PLD-118, at concentrations up to 100 microM, is not metabolized by rat, dog or human liver S9 homogenates and does not inhibit human CYPs in vitro, suggesting little likelihood for interaction of PLD-118 with drugs metabolized by these enzymes.
The regional myocardial uptake and kinetics of 11C-lidocaine, 11C-bupivacaine, and 11C-ropivacaine were examined in the pig, utilizing positron emission tomography to determine whether disproportionate distribution exists among these agents. The three drugs were rapidly distributed to the myocardium and lung with mean peak radioactivities occurring between 0.35 and 0.48 min post-injection in myocardium and 0.35 and 0.65 min in lung. Radioactivities peaked later in skeletal muscle than in the myocardium and lung, occurring between 1.1 and 2.7 min post-end injection. Blood radioactivities for bupivacaine and ropivacaine were significantly higher than those of lidocaine, whereas myocardial, lung, and muscle uptakes for the three agents were not significantly different. Myocardium-blood partition coefficients were similar for bupivacaine and ropivacaine (0.55 and 0.49 respectively), while it was three times higher for lidocaine (1.4). A similar relationship existed for skeletal muscle- and lung-blood partition coefficients. Bupivacaine and ropivacaine t1/2z in skeletal muscle were significantly longer than those of lidocaine. The results of this study indicate that the increased cardiotoxicity associated with bupivacaine does not appear to be related to disproportionate distribution in the myocardium when compared to lidocaine and ropivacaine.
The pharmacokinetics of DA-125 were compared after intravenous (i.v.) administration of the drug, 10 mg kg-1, to control male Sprague-Dawley rats (n = 9) and uranyl nitrate-induced acute renal failure (U-ARF, n = 12) rats, or male Sprague-Dawley rats fed on a 23% (control, n = 8) or a 5% (protein-calorie malnutrition, PCM, n = 9) protein diet. After i.v. administration of DA-125, almost 'constant' plasma concentrations of M1, M2, and M4 were maintained from 1-2 h to 8-10 h in all rat groups due to the continuous formation of M2 from M1 and M4 from M3. The plasma concentrations of M3 were the lowest among M1-M4 for all rat groups due to the rapid and almost complete conversion of M3 to M4 and other metabolite(s). The AUCt values of M1 (115 against 82.5 micrograms min mL-1), M2 (33.0 against 23.6 micrograms min mL-1), and M4 (26.3 against 15.1 micrograms min mL-1) were significantly higher in the U-ARF rats than in the control rats. The percentages of i.v. dose excreted in 24 h urine as M1 (under the detection limit against 0.316%), M2 (under the detection limit against 5.58%), and M4 (0.0174 against 0.719%)--expressed in terms of DA-125--were significantly lower in the U-ARF rats than in the control rats, and this could be due to the decreased kidney function in the U-ARF rats. However, the percentages of i.v. dose recovered from the GI tract at 24 h as M1 (0.0532% against under the detection limit), M3 (0.0286% against under the detection limit), and M4 (0.702% against 0.305%)--expressed in terms of DA-125--were significantly greater in the U-ARF rats than in the control rats. All U-ARF rats had ascites, but the concentrations of M1 (0.0320 micrograms mL-1), M2 (0.0265 micrograms mL-1), M3 (under the detection limit), and M4 (0.032 micrograms mL-1) in the ascites from one rat were almost negligible. The plasma concentrations and most of the pharmacokinetic parameters of M1, M2, and M4 were not significantly different between the PCM rats and their control rats.
The pharmacokinetics of M1, M2, M3 and/or M4 were compared after intravenous (i.v.) administration of DA-125 and/or ME2303 to mice (25 mg kg(-1)) and rats (5, 10, 20, 30, and 40 mg kg(-1)). The mean plasma concentrations of M1 were detected up to 8 h after i.v. administration of both DA-125 and ME2303 to mice, and were significantly higher for DA-125 than ME2303; this resulted in a considerably greater AUC (303 against 148 micrograms min mL(-1)) and a considerably slower CL of M1 (69.3 against 136 mL min-1 kg(-1)) after i.v. administration of DA-125. The MRT (371 against 189 min) and CLNR of M1 (68.7 against 136 mL min-1 kg(-1)) were considerably greater and slower, respectively, after i.v. administration of DA-125. The mean plasma concentrations of M2 were detected up to 8 and 4 h after i.v. administration of DA-125 and ME2303, respectively, to mice and were significantly higher for DA-125 than ME2303, resulting in a considerably greater AUC of M2 (148 against 27.1 micrograms min mL(-1)) after i.v. administration of DA-125. The mean plasma concentrations of M3, being the lowest among M1-M4, were detected only up to 15 min after i.v. administration of both DA-125 and ME2303 to mice, and were comparable after i.v. administration of DA-125 and ME2303 to mice. The mean plasma concentrations of M4 were detected up to 8 h after i.v. administration of both DA-125 and ME2303 to mice, and were higher after i.v. administration of DA-125 than ME2303, resulting in a considerably greater AUC of M4 (197 against 61.9 micrograms min mL(-1)) after i.v. administration of DA-125. Similar results on M1 and M2 were also obtained from rats: the mean plasma concentrations of both M1 and M2 were significantly higher after i.v. administration of DA-125, 10 mg kg(-1), than after ME2303. The plasma concentrations of M1, M2, and M4, and hence their AUCs, were significantly higher after i.v. administration of DA-125, 5, 10, 20, 30, and 40 mg kg(-1), to rats than after ME2303: the mean plasma concentrations of M2, approximately 0.1-0.4 micrograms mL(-1), were maintained from 30 min to 8-10 h after i.v. administration of DA-125, 20, 30, and 40 mg kg(-1), to rats; the plasma concentrations of M3 were the lowest among M1-M4 at all DA-125 doses; and those of M1 and M4 were maintained for a long period of time. However, after i.v. administration of M2, 5 mg kg(-1), to rats, the mean plasma concentrations of M2 were detected up to 60 min with a mean terminal half-life of only 38.8 min, and the concentrations of M3 were negligible. After i.v. administration of M3, 5 mg kg(-1), to rats, the mean plasma concentrations of M3 were detected up to 15 min; the plasma concentrations of M4, reaching their peak at 5 min, decayed more slowly and were higher than those of M3. The AUC of M4 after i.v. administration of M3, 5 mg kg(-1), was comparable to that after i.v. administration of M4, 5 mg kg(-1), to rats, suggesting that M4 is formed fast and almost completely from M3. M1 was not detected in plasma after i.v. administration of either M2 or M3 to rats. After i.v. administration of M4, 5 mg kg(-1), to rats, the mean plasma concentrations of M4 decayed fast with a mean terminal half-life of 43.9 min and neither M2 nor M3 were detected in plasma. The following disposition mechanisms for M1, M2, M3, and M4 after i.v. administration of DA-125 to rats could be obtained from the above data; (i) the maintenance of plasma concentrations of M2 for a longer period of time after i.v. administration of DA-125 than those after i.v. administration of M2 could be due to the continuous formation of M2 from M1; (ii) the lowest plasma concentrations of M3 among M1-M4 after i.v. administration of DA-125 could be due to the fast and almost complete information of M4 from M3 as soon as M3 is formed from M1, and not due to the fast renal excretion of unchanged M3; (iii) M4 was exclusively and continuously formed from M3 and the formation of M4 from M2 was negligible; and (i.v.) reversible me
The pharmacokinetics of M1-M4, the metabolites of a new anthracycline antineoplastic agent, DA-125, were compared after intravenous (i.v.) administration of DA-125, 15 mg kg-1, to rats pretreated with enzyme inducers, such as phenobarbital (PBT, n = 14) and 3-methylcholanthrene (MCT, n = 15), or enzyme inhibitors, such as SKF-525A (SKT, n = 11) and chloramphenicol (CMT, n = 15), and to their control rats (n = 15 for PBC, CMC or SKC, and n = 11 for MCC). After i.v. administration of DA-125, the plasma concentrations of both M1 and M2 declined slowly from 1 to 2 h onwards to 8 h in all groups of rats due to the continuous formation of M2 from M1. The AUC0-8 h of M1 (47.1 versus 7.85 micrograms min mL-1) and M2 (20.7 versus 44.3 micrograms min mL-1) decreased significantly in the PBT group compared to those in the PBC group. However, the corresponding value of only M1 (74.6 versus 89.9 micrograms min mL-1) decreased significantly in the MCT group. The above data indicate that metabolism of M1 is increased by pretreatment with both PB and 3-MC, and that of M2 with PB, but not with 3-MC. The AUC0-8 h of both M1 (126 versus 78.5 micrograms min mL-1) and M2 (69.2 versus 44.3 micrograms min mL-1) increased significantly in the SKT group compared to the SKC group. However, the corresponding values were not significantly different between CMC and CMT groups. The above data indicate that the metabolism of both M1 and M2 is inhibited by pretreatment with SKF-525A, but not with CM.
The purpose of this study was to apply a replicate design approach to a bioequivalence study of amoxicillin/clavulanic acid combination following a 250/125 mg oral dose to 23 subjects, and to compare the analysis of individual bioequivalence with average bioequivalence. This was conducted as a 2-treatment 2-sequence 4-period crossover study. Average bioequivalence was shown, while the results from the individual bioequivalence approach had no success in showing bioequivalence. In conclusion, the individual bioequivalence approach is a strong statistical tool to test for intra-subject variances and also subject-by-formulation interaction variance compared with the average bioequivalence approach.
A bolus injection multiple blood sampling method was developed for the simultaneous measurement of blood and plasma clearance of three radiopharmaceuticals in rats. Technetium-99m mercaptoacetyltriglycine ([(99m)Tc]MAG(3)) and iodine-131-orthoiodohippurate ([(131)I]OIH) were used as makers of effective renal blood flow (ERBF), and iodine-125 iothalamate ([(125)I]IOT) was used as a marker of glomerular filtration rate (GFR). These methods can be easily performed in rats without arterial catheterization. Tissue biodistribution was studied in four groups of rats subjected to the following: group A, renal pedicle isolation (sham-operated); group B, ligature of one kidney pedicle; group C, ligature of both renal pedicles; and group D, ligature of both kidney pedicles and the bile duct. Renal clearance of [(99m)Tc]MAG(3) was greater than [(131)I]OIH and both agents were cleared faster than ([(125)I]-IOT). Either of the two markers of ERBF may be used in experimental studies, but it should be borne in mind that these are relative measurements of kidney performance. [(99m)Tc]MAG(3) and [(125)I]-IOT showed bile excretion in healthy rats, so they cannot completely fulfill the requirements for use as markers of ERBF. When renal function was impaired experimentally, [(99m)Tc]MAG(3) and [(125)I]-IOT were excreted in bile and [(131)I]OIH was secreted in the intestine. Thus, while the markers of ERBF and GFR may be reliable under normal physiological conditions, they may give progressively more erroneous values as renal function deteriorates.
Growth factors have proved to be an effective therapeutic strategy. However, some controversies have arisen concerning their efficacy in topical wound treatments. Stabilization of epidermal growth factors at the wound site and long-lasting receptor occupancy are important factors for wound repair. This study evaluated the cumulative profiles of two jellies containing 10 or 20 microg of 125I-rhEGF per gram of jelly, in a rat full-thickness skin lesion model. The prolonged time-courses at the wound sites for both strengths compared with saline solutions previously evaluated using a similar skin lesion model are reported. It seems that these two topical formulations that provide more sustained amounts of 125I-rhEGF over the period of sampling, would probably achieve the required wound healing response in terms of cell proliferation, collagen deposition and protein synthesis. Further studies need to be developed in order to elucidate whether such an in vivo disposition pattern is consistent with an earlier and stronger promotion of wound healing events.
Bromelain is a sulphydral protease, derived from the stem and fruit of pineapples. Semi-purified preparations of bromelain are used in the treatment of inflammation and oedema. There is however no unequivocal proof of the absorption of the enzyme after oral administration. In this study, 125I-bromelain was administered orally to rats and blood sampled at various times. The total radioactivity, the TCA precipitable 125I-compounds and the molecular weight profile of 125I-proteins in the plasma were determined. A maximum level, equivalent to 270 ng ml-1 bromelain was found at 1 h after administration. Approximately 40 per cent of the 125I in plasma could be precipitated by 10 per cent trichloroacetic acid. Electrophoretic analysis showed one major peak of radioactivity in the plasma samples, with a molecular weight of 26-32,000 daltons. This is identical to the main molecular weight fraction in the Bromelain mixture and corresponds to the molecular weight of the purified enzyme. In the 1 h plasma sample this peak contained 0.003 per cent of the administered dose per millilitre.
3M has formulated a new chlorofluorocarbon-free (CFC-free) beclomethasone dipropionate (BDP) metered-dose inhaler (MDI) with the use of the propellant HFA-134a (HFA). Lung deposition studies demonstrated that the HFA BDP MDI delivers to the lungs approximately 56% of the BDP dose (ex-adaptor), a substantially higher percentage than the 5-30% delivered by conventional CFC BDP MDIs. As new sensitive bioanalytical methods are becoming available to quantitate systemic levels of inhaled corticosteroids, pharmacokinetic evaluations are emerging as sensitive and reproducible methods that can be used as a complement to the data obtained from lung deposition studies to assess and compare the performance of MDIs. The present study was designed to determine the beclomethasone (BOH) availability of oral BDP relative to inhaled HFA BDP as a first step to alloy MDI product comparisons in the future. Forty mild asthmatic patients completed this open-label, randomized, single-dose, two-period crossover study. Each patient received an oral dose of BDP (0.2, 0.5, 1, 2 or 5 mg) in one period and an inhaled dose of BDP (0.2 or 0.8 mg) in the other period, with four patients allocated to each of ten different treatment sequences. The BOH availability of orally administered BDP was approximately 40% relative to inhaled HFA BDP. In addition, the fraction of an oral dose that reaches the systemic circulation was estimated from the 40% relative availability and previous lung deposition data to be 0.26. These estimated pharmacokinetic parameters will be used in the future to further characterize the pharmacokinetics of inhaled BDP and to compare the performance of different MDI products.
BI 1356 (INN: linagliptin) is an inhibitor of dipeptidyl peptidase-4 (DPP-4). This study investigated whether saturable binding of BI 1356 to its target DPP-4 occurs in tissues and whether drug accumulation occurs at these sites in vivo. In order to test these hypotheses, the tissue distribution of BI 1356 was determined in wild-type and DPP-4 deficient rats at different dose levels by means of whole body autoradiography and measurement of tissue radioactivity concentrations after single i.v. dosing of [(14)C]-radio labeled BI 1356. The accumulation behavior of drug-related radioactivity in tissues was further explored in an oral repeat dose study. Tissue levels of [(14)C]BI 1356 related radioactivity were markedly lower in all investigated tissues of the DPP-4 deficient rats and the difference of the dose-dependent increase of radioactivity tissue levels between both rat strains indicates that tissue distribution at low doses of BI 1356 is dominated by binding of BI 1356 to DPP-4 in tissues. As the binding to DPP-4 is strong but reversible, the tissue binding results in a long terminal half-life in several tissues including plasma. The binding capacity to DPP-4 is, however, limited. In the rat, saturation of DPP-4 binding is suggested at an intravenous dose above 0.01-0.1 mg/kg [(14)C]BI 1356. As the DPP-4 binding capacity is saturated already at low doses, accumulation of BI 1356 in tissues is unlikely, despite the long persistence of low amounts in the body.
Linagliptin (BI 1356) is a novel dipeptidyl peptidase-4 (DPP-4) inhibitor in clinical development for the treatment of type 2 diabetes. It exhibits non-linear pharmacokinetics and shows concentration-dependent plasma protein binding to its target, DPP-4. The aim of this study was to investigate the impact of saturable binding of linagliptin to plasma and tissue DPP-4 by comparing the pharmacokinetics of linagliptin in wildtype and DPP-4 deficient Fischer rats using non-compartmental and model-based data analysis. The non-compartmental analysis revealed a significantly reduced AUC in DPP-4 deficient rats compared with wildtype rats when single intravenous doses <or=1 mg/kg were administered, but the exposure was similar in both strains at higher doses. The terminal half-lives were significantly shorter in DPP-4 deficient rats compared with wildtype rats. For doses <or=1 mg/kg, DPP-4 deficient rats exhibited linear pharmacokinetics, whereas the pharmacokinetics of wildtype rats was non-linear. In the model-based analysis these differences could be accounted for by assuming concentration-dependent protein binding in the central and one peripheral compartment in wildtype rats. In the model, disposition parameters for unbound linagliptin were assumed to be identical in both rat strains. Simulations with different doses of linagliptin and different concentrations of binding sites further illustrated that the interdependence of linagliptin and DPP-4 in plasma and in the periphery has a major influence on the disposition of linagliptin in wildtype rats. In conclusion, the study showed that the concentration-dependent binding of linagliptin to its target DPP-4 has a major impact on the plasma pharmacokinetics of linagliptin.
The pharmacokinetics of the new angiotensin converting enzyme (ACE) inhibitor benazepril.HCl were evaluated in healthy male volunteers. The single dose kinetics were established from data of 62 subjects receiving an oral 10 mg dose of the drug. The steady state kinetics were investigated in 15 subjects after once-daily oral doses of 5, 10 or 20 mg. The compound is a prodrug which, on absorption, is hydrolysed to the pharmacologically active metabolite benazeprilat. Thus, plasma concentrations and urinary excretion of parent compound and active metabolite were determined. Benazepril.HCl was rapidly absorbed (tmax = 0.5 h) and rapidly eliminated from plasma (t1/2 = 0.6 h). Only trace amounts were excreted unchanged in urine. The drug was rapidly metabolized to benazeprilat (tmax = 1.5 h). The elimination of the metabolite from plasma was biphasic. About 80 per cent of benazeprilat formed was eliminated within 24 h (t 1/2 = 2.7 h), whereas the terminal phase (t1/2 = 22.3 h) controlled a minor amount of elimination. About 17 per cent of dose was excreted in the 24-h urine as benazeprilat. The drug disposition did not change during repeated oral dosing and only small accumulation of the metabolite occurred. The accumulation ratio was 1.20 for AUC and 1.24 for urinary excretion. The effective half-life for accumulation was estimated at about 10-11 h. The comparison with other ACE inhibitors showed similarities but also marked differences with respect to the drug kinetics and excretion.
The pharmacodynamics, pharmacokinetics, metabolism, and excretion of 14C-sumatriptan have been studied in the beagle dog following administration by the intranasal and other routes. The pharmacological response which was monitored, an increase in carotid arterial vascular resistance, correlated with the plasma levels of unchanged sumatriptan following intranasal, intravenous, or intraduodenal administration to the anaesthetised dog. The pharmacokinetics and metabolism of sumatriptan were then confirmed in conscious male and female dogs. Intranasal administration of 14C-sumatriptan resulted in rapid absorption of part of the dose. The overall bioavailability of sumatriptan was 40-50%. Sumatriptan was eliminated from plasma with a half-life of 1.5 or 1.9 h after intravenous or intranasal dosage respectively. Radioactivity was largely excreted in urine (up to 75% of the dose) with small amounts in the bile and faeces after intravenous and intranasal dosing, as sumatriptan and a major metabolite. The results from these studies suggest that intranasal administration provides a viable method for delivering sumatriptan to the systemic circulation.
Tissue distribution studies, utilizing whole-body autoradiography and organ dissection techniques, were conducted in male Fischer 344 rats following the oral administration of 14C-dapoxetine HCl, a potent serotonin reuptake inhibitor. The preliminary study using whole-body autoradiography proved invaluable in locating radioactivity in an organ not usually harvested in a tissue distribution study, namely the preputial gland. Selected organs, based on whole-body autoradiography findings, were dissected from rats and analyzed for radiocarbon content by liquid scintillation counting and for parent drug and N-dealkylated metabolites by extraction and HPLC analysis. Highest concentrations of radiocarbon were observed in the organs of absorption and elimination (ileum, cecum, stomach, duodenum, liver, colon, and kidney) but notable quantities were observed in the lung and preputial and Harderian glands. Most tissues had returned to background radioactive levels 72 h after dosing but persistent concentrations of radiocarbon were present in the preputial gland and liver one week after the single dose of 14C-dapoxetine.
Analysis by HPLC demonstrated the presence of parent drug and N-desmethyl metabolite (nor-dapoxetine) in those organs examined; however, the majority of the radioactivity remained unidentified.
Palonosetron (Aloxi(R), Onicit(R)) is a potent, single stereoisomeric 5-HT(3) receptor antagonist developed to prevent chemotherapy-induced nausea and vomiting. The pharmacokinetics and metabolic disposition of a single intravenous [(14)C]-palonosetron (10 microg/kg, 0.8 microCi/kg) bolus dose were evaluated in six healthy volunteers (three males, three females) using serial blood, plasma, urine and fecal samples obtained over 10 days. The safety, tolerability and cardiac effects were assessed. Radiolabeled metabolic characterization revealed that unchanged palonosetron accounted for 71.9% of the total radioactivity in plasma over 96 h, with an extensive distribution volume (8.34 l/kg) and mean plasma elimination half-life of 37 h. Approximately 83% of the dose was recovered in urine ( approximately 40% as unchanged drug, with 50% metabolized; M9 and M4 were the major metabolites) and 3.4% in feces. Hydrolysis of urine samples suggests that the metabolites are not beta-glucuronide or sulfate conjugates of the parent drug or metabolites. The blood to plasma concentration ratio of the total radioactivity was 1.2, on average, indicating little selective partitioning in erythrocytes. Palonosetron was generally well tolerated; headache was the most frequently reported adverse event. Electrocardiograms and 72 h Holter monitoring revealed no clinically significant changes. Palonosetron circulates in plasma mainly as the parent drug. Renal elimination is the primary excretion route, with parent drug and metabolites M9 and M4 accounting for the majority of palonosetron disposition. These results indicate that both renal and hepatic routes are involved in the elimination of palonosetron from the body.
Aclidinium bromide is a novel, inhaled long-acting muscarinic antagonist with low systemic activity developed for the treatment of COPD. It is an ester compound rapidly hydrolysed in plasma into inactive alcohol and acid metabolites. In this Phase I, open-label study, the rates and routes of elimination of radioactivity following intravenous administration of [¹⁴C]-aclidinium bromide were determined. The metabolites of aclidinium were also characterized and identified in plasma and excreta. Twelve healthy males were randomized (1:1) to receive a single intravenous 400 µg dose of [phenyl-U-¹⁴C]- or [glycolyl-U-¹⁴C]-aclidinium bromide (via 5 min infusion) to label alcohol or acid metabolites of aclidinium, respectively. Safety and tolerability were assessed over a 9-day period. Following intravenous administration, the parent compound was rapidly hydrolysed into its acid and alcohol metabolites. Primary excretion routes for [phenyl-U-¹⁴C]- and [glycolyl-U-¹⁴C]-aclidinium were renal (urine: 65% and 54%, respectively; feces: 33% and 20%, respectively), with 1% excreted as unchanged aclidinium. A total of three treatment-emergent adverse events in two subjects were reported and were related to infusion site pain. Overall, aclidinium is rapidly hydrolysed into two main metabolites, which are predominantly excreted in urine. Aclidinium bromide 400 µg administered intravenously was safe and well tolerated in healthy subjects.
The disposition of the enantiomers of oxaprotiline has been investigated after single 100 mg oral doses of racemic 14C-labelled oxaprotiline X HCl in two healthy subjects. Absorption was complete. Peak blood concentrations of total 14C were 804 and 1010 ng equiv. g-1 after 4-6 h in the two subjects. After 9 days 85 and 80 per cent of the dose were excreted in urine, and a total of 93 and 87 per cent were found in the excreta. Mean peak blood concentrations of unchanged S(+)- and R(-)-oxaprotiline amounted to 25 and 10 ng g-1 before, and 474 and 422 ng g-1 after acid hydrolysis (free plus O-glucuronide). The mean blood half-lives of the S(+) and R(-) isomers were 22 and 23 h. Direct O-glucuronidation is the major metabolic pathway and N-demethylation a minor one. The former is more marked with the S(+) isomer and the latter with the R(-) isomer. For oxaprotiline, the AUC-ration of S(+) to R(-) was 2.2 before and 1.4 after hydrolysis. For desmethyl oxaprotiline the corresponding ration was 0.8 after hydrolysis. In urine, 0.8 and 0.5 per cent of total 14C were present as unchanged S(+)- and R(-)-oxaprotiline. After acid hydrolysis of the O-glucuronides, the enantiomers account for 44.7 and 37.1 per cent. The O-glucuronides of S(+)- and R(-)-desmethyl oxaprotiline account for 4.6 and 5.7 per cent.
In vitro studies: In CaCo-2 cell monolayers the β-nonapeptide H(β-HAla-β-HLys-β-HPhe)3-OH·4HCl (1), 14C-labeled on both C atoms of the CH2–CO moiety of the central β-HPhe residue, showed a low intrinsic permeability (<1%) and is subject to a prominent efflux system. The β-peptide (1) binds to human and rat plasma protein in vitro independent of the concentration of 1 and of the species (30–36% bound fraction at 50, 500, and 5000 ng/ml), and has only low affinity for the corresponding blood cells (less than 5% of compound 1 in blood cells).
In vivo studies: The in vivo pharmacokinetic characteristics after i.v. administration of 5 mg/kg (to male rats and to bile-duct-operated rats) were: (i) negligible in vivo biotransformation of 1 (in urine, plasma and feces unchanged 1 represented virtually the only compound-related molecule); (ii) rapid initial decline (0–8 h post dose) of levels of compound 1 in blood and plasma followed by a slower decline (8–96 h post dose); (iii) in non-operated animals after 96 h only 38% of the dose was excreted and after 168 h 49% of the dose was found remaining in the carcass; elimination through the intestine wall represented the major elimination pathway in non-operated animals while in bile-duct-cannulated animals biliary excretion was not found to contribute substantially to elimination (iv) quantitative whole-body autoradioluminography (QWBAL) investigations revealed that the kidney was by far the most important target organ of distribution; other tissues with high concentrations of compound-related radioactivity were cartilage, lymph nodes, and liver, whereas lowest levels were found in white fat and in the brain. After p.o. administration (10 mg/kg) negligible radioactivity was observed in the systemic circulation, indicating negligible absorption; essentially the entire oral dose was recovered unchanged in feces collected over a period of 96 h. Copyright
Three healthy male subjects received single 100 mg oral doses of carprofen containing 20 microCi of 14C-carprofen. Venous blood samples were drawn during the first 48 h after the dose and urine and faeces were collected for 120 h. Concentrations of carprofen and its metabolites in body fluids were determined by TLC and mass spectral analysis. After a lag time of 0.3 +/- 0.1 h (mean +/- S.D.), carprofen was absorbed rapidly and peak concentrations in the plasma were reached in 2.7 +/- 1.3 h. The 14C plasma concentrations declined in a biphasic fashion. The mean half-lives of the initial (alpha) and terminal (beta) phases were 1.1 h and 20.6 +/- 6.1 h, respectively. Biotransformation to a glucuronide metabolite appeared to be the major mechanism of carprofen clearance. In 48 h 74.0 per cent of administered radioactivity was recovered in urine and 14.1 per cent was recovered in faeces. A glucuronide of carprofen comprised 85.0 per cent of the radiolabelled compounds in urine. The remaining radioactivity was comprised of parent drug (12.0 per cent) and un unidentified acid-labile conjugate of the parent drug (3.0 per cent). This pattern of metabolism and excretion is different from that in the dog and rat and may explain species differences in drug activity and toxicity.
The absorption and disposition of roquinimex (Linomide) were studied in four male and two female healthy volunteers. The subjects received a single oral aqueous solution of 14C-labelled roquinimex, about 0.1 mg/kg, after an overnight fast. Blood samples were taken and urine and faeces were collected for 10 days after dosing. The plasma, urine and faeces concentrations of roquinimex and metabolites were determined by high-performance liquid chromatography (HPLC) with radiochemical detection. The metabolites were identified by HPLC-mass spectroscopy (MS). The plasma concentration-time profiles of roquinimex exhibited a rapid absorption followed by a bi-exponential disposition. A secondary peak was observed between 6 and 8 h, indicating enterohepatic circulation (EHC) of roquinimex. The terminal disposition half-life was estimated as 27 h. The primary metabolic pathways of roquinimex were hydroxylation, demethylation and conjugation. The major compound in plasma was roquinimex; metabolites were only occasionally detected. In urine and faeces, roquinimex accounted for 2% of the dose and conjugated and hydroxylated metabolites each accounted for about 30% of the dose. A model was derived for the plasma concentrations of roquinimex and the amount of urinary excreted roquinimex to take into account EHC. This model improved the goodness-of-fit according to common goodness-of-fit criteria. The values of the pharmacokinetic parameters were similar using compartmental and non-compartmental methods, indicating that the contribution of EHC of roquinimex is of minor importance in the evaluation of the pharmacokinetics of roquinimex.
The mass balance of 14C bismuth sucrose octasulfate (BISOS) was investigated in eight male Sprague-Dawley rats after single oral doses of 1.0 g kg-1. Bismuth and radioactivity were monitored in blood, urine, and feces for up to 144 h post-dose, while kidneys, brain, liver, and lungs were assayed for bismuth at 144 h post-dose. In a separate experiment, bismuth was monitored in bile of bile-duct-cannulated animals for 48 h post-dose. Fecal excretion of bismuth averaged 95.8 +/- 5.30% bismuth dose, while 99.2 +/- 3.63% of the radiolabel was excreted in feces. Urinary excretion of bismuth averaged 0.051 +/- 0.028% bismuth dose, and 1.83 +/- 1.08% radioactive dose. Biliary excretion of bismuth averaged 0.0003 +/- 0.0006% bismuth dose, and 0.026 +/- 0.030% radiolabeled dose. An average 0.005 +/- 0.002% of the bismuth dose was present in kidney, liver, and lung. Bismuth levels in brain were below quantifiable limits. Though BISOS contains 57.3% by weight of bismuth, peak blood concentrations of bismuth were three orders of magnitude lower than for BISOS equivalents (Cmax for BISOS averaged 110 +/- 55.4 micrograms eq mL-1, while for bismuth it was 26.1 +/- 10.3 ng mL-1). This data indicates that bismuth dissociates from sucrose octasulfate, probably during the absorption phase, and exhibits differential pharmacokinetic characteristics from sucrose octasulfate. The low biliary and urinary excretion of both bismuth and BISOS equivalents is indicative of low systemic absorption. Greater than 96% recovery in feces, bile, and urine indicates that mass balance was achieved following oral administration.
The metabolism and biliary excretion of 14C-dideoxyinosine (14C-ddI) has been investigated using the in situ perfused rat liver (PRL) preparation. After 2 h of perfusion through the liver, approximately 70-75 per cent of the total 14C-radiolabel was recovered in the perfusion medium, less than 1 per cent was excreted in bile and 15-18 per cent was retained in the liver. Hepatic clearance of ddI was 1.5 +/- 0.1 ml min-1 and half-life for the elimination of ddI from the medium was 22.9 +/- 2.0 min (n = 3). Hepatic extraction was estimated to be 7.5 per cent. HPLC analysis of the effluent perfusate indicated that ddI was metabolized to hypoxanthine, xanthine, uric acid, and to a polar metabolite which was tentatively identified as allantoin. Approximately 60-65 per cent of the ddI dose was converted to allantoin after 2 h of perfusion. Of the other three metabolites, uric acid levels increased to 20-30 per cent of the dose after 45 min and declined to about 5 per cent of the dose by the end of the perfusion period. Levels of hypoxanthine and xanthine were low and both compounds were not detected in the perfusate after 45 min post-infusion. In bile, the major peak, which accounted for about 50 per cent of the 14C-radiolabel co-eluted with the putative metabolite, allantoin (0.4 per cent of the dose). Uric acid (0.06 per cent of the dose) was the only other metabolite detected in bile. These results suggest that biliary excretion is a minor pathway for the elimination of ddI. Furthermore, ddI is rapidly cleared and metabolized by the liver to hypoxanthine, xanthine, uric acid, and to allantoin.
The pharmacokinetic profile of 14C-etretinate, a retinoid that is effective in the treatment of psoriasis, was studied in six healthy male volunteers and two biliary T-tube patients. Following a 100 mg oral dose of 14C-etretinate (20 microcurie), etretinate and its major blood metabolites (etretin, isoetretin) were measured by HPLC and total carbon-14 was measured in blood, bile, urine, and feces by liquid scintillation counting. Etretinate was extensively metabolized in healthy volunteers and in T-tube patients. During the absorption phase, 75 per cent of the total radioactivity in the blood could be accounted for as etretinate, etretin, and isoetretin whereas these compounds accounted for only approximately 12 per cent of the blood radioactivity in T-tube patients over the same time period. The blood concentrations of etretinate, etretin, and isoetretin appeared to be substantially reduced in T-tube patients compared to those in healthy volunteers. A higher proportion of the total drug was excreted in the feces and bile of the T-tube patients (84 per cent) than in the feces of healthy volunteers (62 per cent). The major factor responsible for the observed decrease in etretinate blood concentrations following biliary cannulation appears to be the reduced absorption of etretinate due to the elimination of solubilizing bile salts in the duodenum. Carbon-14 related material was detected in urine and feces for as long as 3 weeks in healthy subjects supporting the previous observation that a long terminal elimination half-life exists for etretinate, even following a single dose of the compound.
A randomized crossover study was conducted on 26 healthy Arab males to compare the bioavailability of two formulations of fluconazole 150 mg capsules, Fluconazole™ (test) and Diflucan® (reference). The formulations were administered after an overnight fast with a washout period of 2 weeks. Twenty blood samples (per period) were collected over 168 h, plasma fluconazole concentrations were determined by locally validated high performance liquid chromatography (HPLC) assay and pharmacokinetic parameters were analysed by the standard non-compartmental method.
The mean ± SD maximum concentration (Cmax), time to reach maximum concentration (Tmax), area under the curve (AUC0→t and AUC0→∞) and elimination half-life (t1/2) were 3.17±0.47 and 3.24±0.59 µg/ml, 2.62±2.01 and 2.65±1.63 h, 149.52±29.49 and 151.36±25.84 µg.h/ml, 163.57±29.9 and 164.89±26.46 µg.h/ml, and 36.81±5.72 and 36.56±5.36 h for the test and reference drug, respectively. These values are similar to previously reported values in other ethnic groups. The parametric 90% confidence intervals on the mean of the difference (test−reference) between the log-transformed values of the two formulations were 95.484% to 101.035%, 96.382% to 101.245% and 94.621% to 102.074% for AUC0→t, AUC0→∞ and Cmax, respectively. The results indicate that the two formulations are equivalent in the rate and extent of absorption. Further, a review of the literature indicates that there is no apparent ethnic variation in the absorption and elimination rates of fluconazole. Copyright
CGS 15873 is a relatively specific dopamine agonist with preferential activity at the presynaptic autoreceptor and therefore may represent a novel agent for the treatment of schizophrenia and/or Parkinson's disease. Several metabolites have been identified in the rat and monkey using an isotopically enriched dosing solution and pattern recognition techniques coupled with GC/MS and LC/MS. In this study, the metabolism of CGS 15873 was investigated in man using these same techniques. In urine, specific isotope clusters were found that matched the dosing solution pattern. Three metabolites were identified: an O-glucuronide conjugate of the parent drug, N-despropyl CGS 15873, and a keto metabolite of CGS 15873. Thermospray LC/MS allowed for the direct confirmation of the conjugated metabolite. GC/MS required derivatization but afforded greater sensitivity compared to LC/MS.