Averaging pharmacokinetic parameter estimates from experimental studies: statistical theory and application

Method of variability optimization in pharmacokinetic data analysis

For many drugs administered per os, high variability in the concentration–time (C–T) values from first sampling to the phase of distribution may cause difficulty in pharmacokinetic analysis. Therefore, the aim of this study was to propose a method of transformation of C–T data, which would allow significantly reducing the standard deviation (SD) value of observed concentrations, without a statistically significant influence on the value of the mean for each sampling point in group. In the presented study, the lowest value of relative standard deviation of concentrations observed in the elimination phase and the value of precision of the used analytical method, were used to optimize the arithmetic, geometric means, median, and the value of SD obtained after single oral administration of itraconazole in human subjects. Non-compartmental modeling was used to estimate pharmacokinetic parameters. The analysis of SD pharmacokinetic parameters after C–T value optimization indicated more than twice the lower value of SD. After transforming the itraconazole data, lower variability of concentration data gives more selective pharmacokinetics profile in absorption and early distribution phase.

Pharmacokinetics of dexmedetomidine administered intravenously in isoflurane-anesthetized cats

OBJECTIVE

To determine the pharmacokinetics of dexmedetomidine administered as a short-duration IV infusion in isoflurane-anesthetized cats.

ANIMALS

6 healthy adult domestic female cats.

PROCEDURES

Dexmedetomidine hydrochloride was injected IV (10 μg/kg over 5 minutes [rate, 2 μg/kg/min]) in isoflurane-anesthetized cats. Blood samples were obtained immediately prior to and at 1, 2, 5, 6, 7, 10, 15, 30, 60, 90, 120, 240, and 480 minutes following the start of the IV infusion. Collected blood samples were transferred to tubes containing EDTA, immediately placed on ice, and then centrifuged at 3,901 × g for 10 minutes at 4°C. The plasma was harvested and stored at -20°C until analyzed. Plasma dexmedetomidine concentrations were determined by means of liquid chromatography-mass spectrometry. Dexmedetomidine plasma concentration-time data were fitted to compartmental models.

RESULTS

A 2-compartment model with input in and elimination from the central compartment best described the disposition of dexmedetomidine administered via short-duration IV infusion in isoflurane-anesthetized cats. Weighted mean ± SEM apparent volume of distribution of the central compartment and apparent volume of distribution at steady-state were 402 ± 47 mL/kg and 1,701 ± 200 mL/kg, respectively; clearance and terminal half-life (harmonic mean ± jackknife pseudo-SD) were 6.3 ± 2.8 mL/min/kg and 198 ± 75 minutes, respectively. The area under the plasma concentration curve and maximal plasma concentration were 1,061 ± 292 min•ng/mL and 17.6 ± 1.8 ng/mL, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

Disposition of dexmedetomidine administered via short-duration IV infusion in isoflurane-anesthetized cats was characterized by a moderate clearance and a long terminal half-life.

Multiple dose pharmacokinetics of fiduxosin under fasting conditions in healthy elderly male subjects

Selective alpha1a-adrenoceptor antagonists are effective agents for treatment of benign prostatic hyperplasia, a disorder occurring in middle-aged and elderly males. The objective of this study was to determine the pharmacokinetics of fiduxosin, a novel alpha1a-adrenoceptor antagonist, following multiple dose administration. This was carried out in a Phase I, randomized, double-blind, placebo-controlled, parallel group, multiple oral dose study of fiduxosin. Single once-daily oral doses of 30, 60, 90 or 120 mg of fiduxosin or placebo were administered to healthy elderly male subjects (n = 48; 8 active and 4 placebo per dosing group) for 14 consecutive days. Fiduxosin plasma concentration-versus-time profiles for days 1, 7 and 14 were used to assess fiduxosin pharmacokinetics. Steady state was achieved by day 7. At steady-state mean Tmax (time to maximum plasma concentration), CL/F (apparent oral clearance) and Vbeta/F (apparent volume of distribution) ranges were 1.8-7.8 h, 27.3-47.2 L h(-1) and 846-1399 L, respectively. Tmax and VbetaF were independent of dose. Cmax (maximum plasma concentration), Cmin (minimum plasma concentration) and AUC24 (area under plasma concentration vs time curve from 0 to 24 h) for days 7 and 14 were linearly proportional with dose overthe 30-120 mg/day dose range and were unchanged from day 7 to day 14. It was concluded that fiduxosin multiple-dose pharmacokinetics were dose-independent and time-invariant over the 30-120 mg/day dose range under fasting conditions.