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ABSTRACT: The aim of this case study was to develop a drug-specific absorption model for levothyroxine (LT4) using mechanistic gastrointestinal simulation technology (GIST) implemented in the GastroPlus™ software package. The required input parameters were determined experimentally, in silico predicted and/or taken from the literature. The simulated plasma profile was similar and in a good agreement with the data observed in the in vivo bioequivalence study, indicating that the GIST model gave an accurate prediction of LT4 oral absorption. Additionally, plasma concentration-time profiles were simulated based on a set of experimental and virtual in vitro dissolution data in order to estimate the influence of different in vitro drug dissolution kinetics on the simulated plasma profiles and to identify biorelevant dissolution specification for LT4 immediate-release (IR) tablets. A set of experimental and virtual in vitro data was also used for correlation purposes. In vitro-in vivo correlation model based on the convolution approach was applied in order to assess the relationship between the in vitro and in vivo data. The obtained results suggest that dissolution specification of more than 85% LT4 dissolved in 60 min might be considered as biorelevant dissolution specification criteria for LT4 IR tablets.
Biopharmaceutics & Drug Disposition 02/2012; 33(3):146-59. · 2.07 Impact Factor
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ABSTRACT: Although often necessary for obtaining remission following major depressive disorder, combined antidepressant treatment is frequently associated with drug interactions and enhanced adverse drug effects. We investigated pharmacokinetic interactions following combined fluvoxamine and amitriptyline treatment and their impact on therapeutic efficacy and tolerability. Twenty-two inpatients with major depression [Hamilton Depression Scale (HAM-D) rating > or =18] were treated with either amitriptyline (75 mg/day), fluvoxamine (100 mg/day) or both. Blood samples, for determination of amitriptyline, its major metabolite nortritpyline, and fluvoxamine, were obtained after single dose administration and in steady-state. Therapeutic efficacy was evaluated using HAM-D and adverse drug effects were evaluated using the clinical global impression scale. Following combined treatment, steady-state plasma levels of nortriptyline were significantly decreased compared to monotherapy. HAM-D scores after two-week treatment showed that there was a better response to combined treatment. There was no significant difference in severity of adverse effects among groups. We observed a pharmacokinetic interaction between fluvoxamine and amitritpyline resulting in impaired metabolism of the later. However, no significant impact of the interaction on treatment safety was observed. Moreover, concomitant use of amitriptyline at 75 mg/day and fluvoxamine at 100 mg/day was well tolerated with a more prompt and stronger onset of clinical response compared to monotherapy in patients with major depression.
Journal of Pharmacological Sciences 06/2009; 110(1):98-104. · 2.08 Impact Factor
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ABSTRACT: A selective, sensitive, and simple high-performance liquid chromatographic (HPLC) method was developed for the determination of moclobemide and its two major metabolites, Ro 12-5637 and Ro 12-8095, in human plasma. Sample preparation (0.5 ml of plasma) involved solid-phase extraction (SPE) using Speedisk H(2)O-Philic DVB columns. Separations were performed on a Waters XTerra RP18 column (5 microm, 150 mm x 4.6 mm). The mobile phase consisted of 10 mM KH(2)PO(4) with 1% triethylamine (pH 3.9) and acetonitrile (83:17, v/v), and a flow-rate was 1.2 ml/min. The total run time was 13 min. UV detection was performed at 240 nm. Mean absolute recoveries were > or =90% and the limit of quantification (LOQ) for all analytes was 0.02 mg/l. Calibration curves were linear (r>0.995) over a wide range of the analyte concentrations in plasma; thus, the method is suitable for different clinical studies when large variations in the drug/metabolites concentrations are observed. During a 5-day assay validation procedure the accuracy and precision were tested and proven (relative errors (RE)< or =13%; intra-day coefficient of variation (CV)< or =7%; inter-day CV< or =13%). Many drugs frequently used in the target patient population were evaluated for potential interference in order method selectivity to be ensured. The assay has been used in a clinical pharmacokinetic study to assess steady-state pharmacokinetics of moclobemide and two metabolites in depressive patients on mono- and combined therapy.
Journal of Pharmaceutical and Biomedical Analysis 03/2007; 43(4):1416-22. · 2.97 Impact Factor
