Treatment of isoniazid-resistant tuberculosis with isoniazid, rifampin, ethambutol, and pyrazinamide for 6 months.

SETTING: In 1992 the Seattle-King County Department of Public Health Tuberculosis Clinic began to treat patients with isoniazid-resistant tuberculosis with a regimen of isoniazid, rifampin, pyrazinamide, and ethambutol daily for 6 months. OBJECTIVE: To conduct a review of clinical and bacteriological outcomes of treatment for patients who received the four-drug, 6-month regimen for isoniazid-resistant tuberculosis. DESIGN: A retrospective review of medical records of TB cases meeting the study criteria, a Mycobacterium tuberculosis isolate resistant to isoniazid, and intent to treat with a 6-month course of isoniazid, rifampin, pyrazinamide, and ethambutol. RESULTS: Through December 1999, 44 consecutive patients with isoniazid-resistant, rifampin-susceptible tuberculosis were started on the four-drug, 6-month daily regimen. Among 42 patients followed until completion of therapy, three required changes in the regimen due to side effects. There was one case of drug-induced hepatotoxicity. Among 39 patients with pulmonary involvement, 37 converted sputum cultures from positive to negative within 2 months of starting treatment. There were no treatment failures. On passive follow-up of at least 2 years on all patients, two patients relapsed. The single patient with bacteriological relapse did not develop further drug resistance. CONCLUSION: The regimen of isoniazid, rifampin, pyrazinamide, and ethambutol given daily for 6 months produced successful outcomes when used in a public health tuberculosis clinic as routine therapy for isoniazid-resistant tuberculosis.