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 (Cmax),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 (AUC0-2,4 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).