In vitro susceptibility of Mycobacterium avium to a new macrolide (RU-28965).

The in vitro susceptibility of Mycobacterium avium to RU-28965 alone and in combination with rifampin, isoniazid, and sulfametoxipiridazine was studied by the agar dilution method. The synergistic effect of the RU-28965 with rifampin has been demonstrated. At a concentration of 16 micrograms/ml or lower of RU-28965, 100% of M. avium strains were inhibited. If 2 micrograms/ml of rifampin is added the MIC of RU-28965 is lowered to 0.25 microgram/ml.