Widespread distribution of a single drug rifampicin formulation of inferior bioavailability in South Africa.

A pharmacokinetic study of rifampicin, isoniazid, pyrazinamide and ethambutol in 118 tuberculosis patients revealed low and variable concentrations of rifampicin after 2 months of treatment on standard daily doses. A group of 53 patients exposed to specific batches of formulations containing rifampicin alone showed particularly low and variable levels of the drug. The national drug regulatory authority subsequently withdrew the batches in question, as sufficient bioavailability data had not been submitted after what the manufacturer had considered to be a minor formulation change. The evidence supports initiatives to implement bioavailability testing of new formulations (and of established formulations subsequent to changes in the manufacturing process) prior to distribution. Concerns about the bioavailability of rifampicin-containing products, including those with adequate dissolution profiles, should not be confined to fixed-dose combination anti-tuberculosis drugs, but should also be applied to single drug formulations.