Comparison of isoniazid phenotyping of black and white patients with emphasis on South African blacks.

Black tuberculosis patients from South Africa (S. A.) as well as from Birmingham, Alabama, U.S.A., showed a higher percentage of fast inactivators of isoniazid (INH) than that found in the North American white population, simultaneously sampled. In S. A. blacks, the frequency of fast inactivation was 57.9--59.6%, while in American blacks of Birmingham it amounted to 60.3%; in comparison to the above groups the rate of fast acetylators in Canadian Caucasians was 41.9% and in the USA white population 41.0%. For phenotyping of isoniazid inactivators a urine test was used. In this method the concentrations of INH (including isoniazidhydrazones) as well as acetylisoniazid were determined in the specimens collected 6--8 hrs following a test dose of 10 mg/kg INH.