Acetylator phenotyping of tuberculosis patients using matrix isoniazid or sulphadimidine and its prognostic significance for treatment with several intermittent isoniazid‐containing regimens.

1. The acetylator phenotype of over 600 pulmonary tuberculosis patients treated with intermittent isoniazid‐containing regimens in two controlled clinical trials was determined using either sulphadimidine or a slow‐release isoniazid formulation. 2. Both methods unequivocally classified over 99% of the patients as being either slow or rapid acetylators. 3. Rapid and slow acetylation did not differ in their ability of hydrolyse acetylisoniazid to isonicotonic acid plus monoacetylhydrazine, or to conjugate isonicotinic acid with glycine. 4. Rapid acetylators acetylated the monoacetylhydrazine liberated in vivo more rapidly than slow acetylators, demonstrating that this compound is also polymorphologically acetylated in man. 5. The acetylator phenotype of the patients was without prognostic significance when they were treated on a twice‐weekly basis with isoniazid plus streptomycin plus pyraziniamide, or with isoniazid plus rifampicin. However, when patients were treated once every week for 12 months with isoniazid plus rifampicin, 5% of the rapid acetylators had an unsatisfactory response as contrasted to the complete success of the treatment in the slow acetylators.