Relapse rates in patients treated with dapsone monotherapy and combinations of dapsone and thiambutosine, thiacetazone, isoniazid and streptomycin in the pre-MDT era

Relapse rates were studied in patients from northern Thailand who were started on dapsone monotherapy between 1949 and 1976. Included are a group of patients who, for various reasons, also received combinations of dapsone and thiambutosine, thiacetazone, isoniazid and streptomycin. The overall relapse rate in paucibacillary patients on dapsone monotherapy only was 2.7 per 1000 person-years at risk (PYR) (average observation period 13.9 years). In the multibacillary patients who received dapsone monotherapy only, the relapse rate was 10.5 per 1000 PYR (average observation period 12.4 years). In both groups it was found that 50% of the relapses occurred after the seventh year of follow up. The overall relapse rate in those patients whose treatment included thiambutosine, thiacetazone, isoniazid and/or streptomycin for at least 3 months was 17.9 per 1000 PYR (average observation period 11.9 years). The difference with the multibacillary patients treated with dapsone monotherapy only is not significant. It is concluded that alternative antileprosy drugs included in therapy regimens with dapsone in the pre-MDT era did not result in relapses occurring less often.