Elevated gatifloxacin and reduced rifampicin concentrations in a single-dose interaction study amongst healthy volunteers.

OBJECTIVES Pharmacokinetic drug-drug interactions were investigated between the fluoroquinolone gatifloxacin and a fixed dose combination (FDC) of rifampicin, isoniazid and pyrazinamide. PATIENTS AND METHODS The single-dose pharmacokinetics of the four drugs was evaluated in an open-label three-way cross-over study amongst 22 healthy volunteers following administration of gatifloxacin, the FDC or the two products together. RESULTS Modest but potentially important drug-drug interactions affecting gatifloxacin and rifampicin concentrations were detected. The elimination rate of gatifloxacin was reduced such that the AUC from 0 h to infinity was increased with a geometric mean ratio (GMR) [90% confidence interval (CI)] of 1.14 (1.10, 1.18). Conversely, the AUC from 0 h to infinity for rifampicin was reduced (GMR: 0.81, 90% CI: 0.81, 0.96) when rifampicin, isoniazid and pyrazinamide were given together with gatifloxacin. CONCLUSIONS Studies in patients including pharmacokinetic evaluation at steady state, efficacy and toxicity are required to determine the importance of the interactions for use of the combination of gatifloxacin, rifampicin, isoniazid and pyrazinamide in the treatment of tuberculosis.