Bioequivalence of rifampicin when administered as a fixed-dose combined formulation of four drugs versus separate formulations

A bioequivalence study of the antitubercular drug rifampicin in a four-drug combination (rifampicin, isoniazid, pyrazinamide and ethambutol) and separate formulations of the drugs at the same dose levels was carried out in a group of 22 healthy male volunteers. The investigation was designed as an open crossover study. The drugs were administered once in individual formulations and once in a fixed-dose combination. The WHO-approved protocol was followed according to which six blood samples were collected over a period of 8 h for each volunteer and each experimental session. Pooled urine samples were also collected during the study. Rifampicin and desacetyl rifampicin concentrations in both plasma and urine samples were assessed. Various pharmacokinetic parameters such as AUC0-8 h, Cmax and Tmax were calculated for both rifampicin and desacetyl rifampicin. The results indicated that combined (the four-drug combination) and separate formulations are bioequivalent for rifampicin.