Bioavailability of mifepristone in capsule versus tablet form in healthy nonpregnant women

BackgroundThe study was conducted to assess the bioavailability of two formulations of mifepristone in capsule and tablet forms at a single dose of 75 mg (half the registered dose in China).Study DesignA randomized two-way crossover study was conducted in 18 healthy nonpregnant women. Each subject was orally given a single dose of mifepristone at 75 mg in capsule or tablet form on an alternate basis. Serial blood samples were collected over a period of 96 h and assayed for the plasma concentration of mifepristone by high-performance liquid chromatography. Paired t tests were used to compare the capsule and tablet forms in terms of maximum concentration (Cmax), time to maximum concentration (Tmax) and area under the curve over 96 h (AUC0–96h). Relative bioavailability (capsule/tablet) was derived from AUC0–96h. Bioequivalability was analyzed by two one-sided t tests.ResultsThe major pharmacokinetic parameters were as follows: Cmax values were 1.26±0.38 and 1.25±0.40 mcg/mL, Tmax values were 0.94±0.34 and 0.89±0.47 h, T1/2Ke values were 36.2±21.0 and 33.4±12.3 h and AUC(0–96h) values were 19.7±6.4 and 19.6±9.9 mcg·h/mL for mifepristone in capsule and tablet forms, respectively. No significant difference was observed among these parameters. The relative bioavailability was 109.4±34.8%.ConclusionThis study suggests that the two formulations of mifepristone are bioequivalent, which provides pharmacokinetic evidence for further reducing the dosage of mifepristone in clinical use.