Undesirable side effects of isoniazid and rifampin in largely twice-weekly short-course chemotherapy for tuberculosis.

Between January 1976 and June 1981, 814 patients with pulmonary tuberculosis were treated for 9 months with isoniazid (INH) and rifampin (RIF), daily for 1 month and twice weekly for the other 8 months. Overall success was achieved in 95% of the 586 patients who completed therapy: in 15 patients (2.9%), sputum cultures failed to convert to negative during therapy, and 10 patients (1.7%) have relapsed since stopping the chemotherapy. Major toxic effects occurred in 22 patients; in 14 during the daily phase and in 8 during the twice-weekly phase. Hepatic toxicity occurred in 13 patients during daily and in 5 during twice-weekly treatment, and it was caused by RIF in 5, INH in 10, and was undetermined in 3. Hematologic abnormalities developed in 4 patients: in 1 during the daily and in 3 during the twice-weekly phase. Minor side effects, which were not life threatening, were encountered in 62 patients: in 35 during the daily and in 27 during the twice-weekly therapy. These were gastrointestinal intolerance in 18, drug fever in 27 (including 11 with "flu-syndrome" during twice-weekly administration), cutaneous rashes in 14, and headache, general malaise, and weakness in 3. These side effects were produced by RIF in 43, by INH in 18, and the responsible drug was not identified in 1. Hypersensitivity reactions to twice-weekly administration of RIF were infrequent. Clinical surveillance for toxicity is preferred over routine and regular biochemical monitoring.