Serum concentrations and bioavailability of rifampicin and isoniazid in combination

The bioavailability of rifampicin and isoniazid from formulations containing these drugs in combination has been compared to that from formulations containing either drug alone. No formulation-related differences in either rates or extent of bioavailability were found after administration of each formulation. Mean peak serum concentrations of rifampicin (8.2-11.7 mug/ml) occurring 2 to 4 h after doses of 600 mg, and isoniazid (3.6-4.8 mug/ml) occurring 0.5 to 1 h after doses of 300 mg, were similar to those reported in the literature.