Relative Bioavailability of Rifampicin in Four Chinese Fixed-dose Combinations Compared with Rifampicin in Free Combinations

BACKGROUND: Decreases in the bioavailability of rifampicin (RFP) can lead to the development of drug resistance and treatment failure. Therefore, we investigated the relative bioavailability of RFP from one four-drug fixed-dose combination (FDC; formulation A) and three two-drug FDCs (formulations B, C, and D) used in China, compared with RFP in free combinations of these drugs (reference), in healthy volunteers. METHODS: Eighteen and twenty healthy Chinese male volunteers participated in two open-label, randomized two-period crossover (formulations A and C) or one three-period crossover (formulations B and D) study, respectively. The washout period between treatments was 7 days. Bioequivalence was assessed based on 90% confidence intervals, according to two one-sided t-tests. All analyses were done with DAS 3.1.5 (Mathematical Pharmacology Professional Committee of China, Shanghai, China). RESULTS: Mean pharmacokinetic parameter values of RFP obtained for formulations A, B, C, and D products were 11.42 ± 3.41 μg/ml, 7.86 ± 5.78 μg/ml, 13.05 ± 6.80 μg/ml, and 16.18 ± 3.87 μg/ml, respectively, for peak plasma concentration (C(max)), 91.43 ± 30.82 μg·h(−1) ·ml(−1), 55.49 ± 37.58 μg·h(−1) ·ml(−1), 96.50 ± 47.24 μg·h(−1) ·ml(−1), 101.47 ± 33.07 μg·h(−1) ·ml(−1), respectively, for area under the concentration-time curve (AUC(0−24 h)). CONCLUSIONS: Although the concentrations of RFP for formulations A, C, and D were within the reported acceptable therapeutic range, only formulation A was bioequivalent to the reference product. The three two-drug FDCs (formulations B, C and D) displayed inferior RFP bioavailability compared with the reference (Chinese Clinical Trials registration number: ChiCTR-TTRCC-12002451).