Objective: Gender is usually considered to be one of the factors influencing disposition of drugs, but the evidence available is sometimes conflicting and information for a large number of frequently used drugs is lacking. An evaluation of sex differences in the disposition ofmetronidazole was carried out during a bioequivalence study.
Subjects and methods: Twenty-four volunteers (12 males and 12 females) were included in an open, single-dose, two-sequence, crossover randomized trial with a one-week washout interval. All volunteers received in each period, a single 250 mg dose of one of the two study formulations of metronidazole. Venous blood samples were collected immediately before and at 15 time points in an 48-hour interval after drug administration; metronidazole concentrations were determined by HPLC. Non-compartmental pharmacokinetic analysis was performed and log-transformed AUC(0-infinity) and Cmax were tested for bioequivalence. Sex differences were evaluated by means of a 4-factor (sex, sequence, treatment and period) ANOVA.
Results: The studied formulations were found bioequivalent according to international standards: average 90% confidence interval for AUC(0-infinity) was 98 to 104 and for Cmax 93 to 115. After correction for the administered dose/kg, AUC was about 12% lower in females than in males (p = 0.0388) and, therefore, a higher calculated oral Cl/kg was found in females. Apparent distribution volume, after correction for weight, was significantly higher in males (p = 0.0019). Metronidazole half-life and MRT were shorter in females than in males (p - 0.0014 and p = 0.0002, respectively).
Conclusions: Data obtained in this study suggest that metronidazole clearance in females is about 12% higher than in males although these differences are probably of no clinical relevance.