Mycobacterium tuberculosis resistance to rifampicin and ethambutol: a clinical survey

Ninety-seven cultures of Myco, tuberculosis referred to the Tuberculosis Reference Laboratory, Cardiff during 1972-73 and found to be resistant to rifampicin or ethambutol were studied. Resistance to each drug appeared equally common. Few lower grades of rifampicin resistance occurred, cultures tending to be either fully sensitive or highly resistant. Intermediate grades of ethambutol resistance, however, were common, and a majority of highly resistant cultures were preceded by cultures showing lower grades of resistance. Case-notes were obtained on 84 patients (87%) and revealed no cases of primary resistance. In the three years since first developing resistance 36% of patients died: in the majority tuberculosis was a major cause of death. Half the patients had been prescribed unsatisfactory drug regimens containing rifampicin or ethambutol by their physicians, and only a small minority were considered to have co-operated well. One-third had discharged themselves from hospital against medical advice and only 21% attended clinics regularly. These two factors probably accounted for the development of resistance in most cases.