Relative bioavailability of rifampicin in a three-drug fixed-dose combination formulation

SETTING: In a previous monitoring study of rifampicin (RMP) in tuberculosis (TB) patients treated with a generic formulation of a three-drug fixed-dose combination (3FDC), very low RMP levels were found. This led us to investigate the bioavailability of the product.OBJECTIVE: To investigate the relative bioavailability of RMP from a generic 3FDC formulation used in the Mexican health care system, in comparison to the reference product, in healthy volunteers.DESIGN: Two-period, two-sequence crossover study.RESULTS: Mean pharmacokinetic parameter values obtained for the test and reference product were respectively 3.13 ± 2.01 μg/ml and 9.95 ± 2.66 μg/ml for peak plasma concentration (Cmax), 15.51 ± 9.77 μg.h/ml and 58.03 ± 16.1 μg.h/ml for area under the concentration (AUC) time curve to the last measurable concentration (AUC0-12h) and 17.92 ± 10.66 and 68.43 ± 22.39 μg.h/ml for AUC up to time infinity (AUC0-∞). The test/reference ratio of the means (90%CI) was 25.36% (17.33-37.10) for Cmax, 21.25% (14.61-30.89) for AUC0-12h and 22.08% (15.44-31.56) for AUC0-∞. These results did not meet the criteria for bioequivalence.CONCLUSION: The test product displayed delayed absorption and markedly inferior RMP bioavailability in comparison to the reference product. RMP-containing generic formulations should only be used if their bioavailability has been evaluated to ensure interchangeability with the reference product and to avoid the risk of markedly inferior RMP exposure through the use of such a product.