Elevated serum aminotransferase induced by isoniazid in relation to isoniazid acetylator phenotype.

Of 143 patients with pulmonary tuberculosis receiving isoniazid therapy, 52 (36%) had a transient elevation in serum aminotransferases. Among 74 patients taking isoniazid, rifampicin and streptomycin, 35 (47%) had such an increase, while of 69 patients taking isoniazid, amino-salicylic acid and streptomycin, 17 (24%) did; this difference was significant. Isoniazid therapy could be continued in all patients with the abnormal test results. In 36 of the patients receiving isoniazid, rifampicin and streptomycin, isoniazid and its metabolites were studied in the serum and urine using high-performance liquid chromatography after the oral administration of 10 mg per kg of isoniazid. We had chosen for this test 18 patients with normal aminotransferase levels and 18 with abnormal levels. There were 14 rapid acetylators in the patients with abnormal aminotransferase levels and 7 rapid acetylators in the patients with normal levels; this difference was significant. These results indicate that liver dysfunction is more often caused by an isoniazid/rifampicin regimen, and patients who are rapid acetylators are more susceptible.