Drug-resistant tuberculosis: etiology, management and prevention.

Drug-resistant Mycobacterium tuberculosis inevitably arises from inadequate or inappropriate drug taking or drug prescribing, effectively resulting in monotherapy. This may occur in the patient being treated (acquired resistance) or in a patient who has been infected by another patient with drug resistant tuberculosis (primary resistance). There is some evidence that multidrug-resistant tuberculosis, ie, resistance to both isoniazid and rifampin, is increasing in the United States and in other countries where unsupervised treatment with rifampin has been common. Human immunodeficiency virus (HIV) infection and acquired immune deficiency syndrome (AIDS), although not causing drug-resistant tuberculosis, have certainly magnified the problem, especially in New York City. Treatment of drug-resistant tuberculosis must be based on results of drug susceptibility studies. Patients with isolated isoniazid-resistant tuberculosis respond well to modified short-course therapy with rifampin, ethambutol, and pyrazinamide. Multidrug-resistant disease is more difficult to treat, although most patients will respond to regimens of second-line drugs if the infecting organisms are susceptible to these agents. Drug-resistant tuberculosis can be prevented by accurate identification of patients with newly diagnosed tuberculosis who may be at increased risk of primary drug resistance, the administration of an appropriate treatment regimen to all newly diagnosed patients, the application of fully supervised therapy during at least the initial phase of treatment, the use of combination preparations of drugs, and the proper management of failure and relapse cases.