Study of 39 documented relapses of multibacillary leprosy after treatment with rifampin

Among 39 strains of Mycobacterium leprae isolated from patients with multibacillary leprosy who relapsed after treatment with rifampin (RMP), 22 strains were resistant to RMP and 17 were susceptible. All of the RMP-resistant strains were recovered from patients who had been treated with more than 50 doses of RMP, usually given as monotherapy. RMP-susceptible strains were recovered from only six patients who had received more than 50 doses of RMP, and from 11 patients who had received no more than seven doses. The median time to relapse after the beginning of RMP therapy was 9 years (range 1-12 years) among the patients harboring RMP-resistant strains of M. leprae, and the median time to relapse after discontinuation of RMP treatment was 7 years (range 1-11 years) among the patients harboring RMP-susceptible strains. These data suggest that monotherapy with more than a few doses of RMP can be responsible for the emergence of RMP-resistant strains of M. leprae, thus emphasizing the need to employ RMP only in combination with other effective drugs in the chemotherapy of multibacillary leprosy.