The colorimetric analysis of anti-tuberculosis fixed-dose combination tablets and capsules.

Setting: The perceived need to demonstrate whether or not the actual amounts of rifampicin, isoniazid and pyrazinamide in fixed-dose combination tablets or capsules correspond to their stated drug contents.

Objective: To adapt specific, robust and simple colorimetric methods that have been previously applied to measuring plasma and urinary rifampicin, isoniazid, pyrazinamide and ethambutol concentrations to estimate tablet and capsule drug contents.

Design: The methods were applied to the analysis of 14 commercially manufactured fixed-dose combinations: two capsule and three tablet formulations containing rifampicin and isoniazid; seven tablet formulations containing rifampicin, isoniazid and pyrazinamide; and two tablet formulations containing rifampicin, isoniazid, pyrazinamide and ethambutol.

Results: All the combined formulations contained near to their stated drug contents. Replicate analyses confirmed the excellent precision of the drug analyses.

Conclusion: Such methods are not only rapid to perform but should be practical in many Third World situations with relatively modest laboratory facilities.