Mass phenotyping of isoniazid inactivators by automated determination of acetylisoniazid in urine.

It is established that in treatment of tuberculosis, slow inactivators of isoniazid are more prone to side effects from the drug (1-3), whereas fast inactivators respond less favorably to marginal chemotherapy in which this drug is administered intermittently or for a limited period (4-8). Therefore, phenotyping of patients for isoniazid inactivation became important in the initiation of long-term therapy of tuberculosis (9). This laboratory has introduced a simple screening test for identification of slow and fast acetylators (10, 11). To facilitate phenotyping on a large scale, the procedure used for acetylisoniazid determination was modified and adapted to continuous-flow automation. Here, we describe the method and evaluate its performance.