In-vitro activity of dapsone and two potentiators against Mycobacterium avium complex

The efficacy of dapsone against Mycobacterium avium, M. intracellulare, M. kansasii, M. fortuitum and M. tuberculosis was determined by disc elution in agar. The minimal inhibitory concentration at which 90% of the colony forming units were inhibited (90MIC) by dapsone was 8 mg/l for M. avium, M. intracellulare and M. kansasii and greater than or equal to 32 mg/l for M. tuberculosis and M. fortuitum. The 90MICs were confirmed by culturing these test organisms with dapsone in the BACTEC 460 system. Reduction of the 90MIC from 8 mg/l to 2 mg/l was observed by combining dapsone with either or both of the potentiators tested. The dapsone-potentiator combinations had no effect on the bacteria with 90MICs of greater than or equal to 32 mg/l. The clinical relevance of this drug combination against M. avium complex infections remains to be evaluated.