Isoniazid acetylation rates (phenotypes) of patients being treated for tuberculosis.

Isoniazid therapy could be used more rationally if patients' isoniazid acetylation rates were known. To explore the clinical usefulness of a recently described simple method for acetylator phenotyping, acetylated and free isoniazid were measured semiquantitatively in morning urine specimens from sanatorium in-patients being treated with the drug. The distribution of acetylisoniazid: isoniazid ratios was bimodal. The ratios thus identify rapid and slow acetylators of isoniazid, without disturbing their routine or their therapy. Ratios measured in samples from control subjects who had received a single dose of isoniazid did not discriminate between these phenotypes, and urine from diabetic patients gave false reactions.