Drug susceptibility of Mycobacterium leprae: a retrospective analysis of mouse footpad inoculation results from 1983 to 1997.

We analysed the results of mouse foot pad (MFP) tests performed between 1983 and 1997 in our laboratory for the cases referred with clinical suspicion of relapse/drug resistance. A total of 214 cases, with clinical suspicion of relapse/drug resistance were investigated for susceptibility to the drugs of MDT by MFP inoculation. Among 96 inoculations that showed conclusive results, 81 (84%) were fully sensitive to dapsone, suggesting that most of the clinically suspected relapse is due to drug susceptible Mycobacterium leprae. Of the remaining 15 strains (16%) found resistant to dapsone, 13 (87%) were of high grade resistance and one strain each of intermediate grade and low grade dapsone resistance, suggesting that most of the dapsone resistance is secondary in nature. No case of rifampicin resistance was found. Only one case of combined dapsone and unconfirmed clofazimine resistance was found. No other combined multidrug resistance was observed in our analysis.