Relative bioavailability of isoniazid in a fixed-dose combination product in healthy Mexican subjects.

SETTING: Subtherapeutic plasma isoniazid (INH) concentrations and the development of bacterial resistance may be attributed to poor quality and reduced bioavailability of fixed-dose combination (FDC) formulations. The bioavailability of INH from a generic and that of a branded FDC formulation had not been compared in the Mexican population. OBJECTIVE: To evaluate the bioequivalence of a generic three-drug FDC formulation (3FDC) in comparison with a 3FDC reference with doses of 300 mg INH in 20 healthy Mexican adults, and to generate data regarding the oral relative bioavailability of the drug in this population. DESIGN: A single-dose, randomised-sequence, open-label, two-period crossover study. RESULTS: Both formulations were well tolerated. The pharmacokinetic parameters of INH showed wide inter-individual variability. The average relative bioavailability calculated for maximum serum concentration area under the concentration-time curve (AUC), AUC(0-24h) and AUC(0-∞) of the test 3FDC formulation vs. the 3FDC reference were respectively 64.84% (90%CI 56.01-75.06), 59.05% (90%CI 50.27-69.36) and 57.26% (90%CI 46.93-69.84). CONCLUSIONS: The 3FDC test and reference formulations were not bioequivalent because the 90%CI for the geometric mean ratios did not meet the regulatory requirements for bioequivalence (range 80-125%) based on the rate and extent of absorption.

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 (C(max)), 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 (AUC(0-12h)) and 17.92 ± 10.66 and 68.43 ± 22.39 µg.h/ml for AUC up to time infinity (AUC(0-∞)). The test/reference ratio of the means (90%CI) was 25.36% (17.33-37.10) for C(max), 21.25% (14.61-30.89) for AUC(0-12h) and 22.08% (15.44-31.56) for AUC(0-∞). 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.