Bioequivalence Study of finasteride - Determination In human plasma by high-pressure liquid chromatography coupled to tandem mass spectrometry

Two different finasteride (CAS 98319-26-7) tablet formulations were evaluated for their relative bioavailability (Flaxin(R) tablets 5 mg, as the test formulation vs reference formulation, tablets 5 mg) in 23 healthy male volunteers who received a single 5 mg oral dose of each preparation. The study was open, randomized with a two-period crossover design and a 7-day washout period. Plasma samples were obtained over a 48-h interval. The finasteride concentrations were determined by high-pressure liequid chromatography (HPLC) coupled to tandem mass spectrometry (LC-MS-MS). The analytical method developed has a limit of quantitation (LOQ) of 0.50 ng/ml in plasma. For the quality control the measured concentration was 2.05 +/- 0.14 ng/ml (mean +/- SD, n = 30) with a precision of 6.9% and an accuracy of 2.55% at a concentration of the starting solution of 2.00 ng/ml, while with 20.00 ng/ml starting solution the measured concentrations were 20 +/- 0.80 ng/ml (n = 30) with a precision of 3.81% and an accuracy of 0.09%. From the plasma finasteride concentration vs time curves the following pharmacokinetics parameters were obtained: AUC(0-48), AUC(0-infinity), C-max, C-max/AUC(0-48), k(e), elimination half-life and t(max). Geometric mean test/reference formulations individual percent ratio was 95.71 for AU(0-48 h) and 88.70% for C-max. The 90% confidence interval for the geometric mean of the individual ratio test/reference formulations was 95.70-120.20% for AUC(0-48 h), 94.60-121.30 for AUC(0-infinity) and 88.70-108% for C-max. Since for both C-max or ADC the 90% Cl values are within the interval proposed by the Food and Drug Administration, the test formulation is bioequivalent to the reference formulation for both the rare and extent of absorption after single dose administration.