Determination of the acetylator phenotype using matrix isoniazid.

The development of a simple method for classifying subjects as slow or rapid acetylators is reported. The method is based on determining the ratio of acetylisoniazid to acid-labile isoniazid in the urine 23-24 hours after an oral dose of a slow-release isoniazid formulation. The results obtained when this method was applied to phenotype over 200 East African tuberculosis patients are described. It is suggested that the method would be particularly suitable for classifying tuberculosis out-patients.