EFFICACY OF AZITHROMYCIN AND RIFABUTIN IN PREVENTING INFECTION BY MYCOBACTERIUM-AVIUM COMPLEX IN BEIGE MICE

We investigated the potential of the azalide, azithromycin, and rifabu tin in preventing disseminated infection due to Mycobacterium avium co mplex (MAC) in beige mice. Azithromycin 200 mg/kg, rifabutin (30 mg/kg or 60 mg/kg) were administered by gavage 6 days before mice were chal lenged orally with 10(8) cfu MAC and daily for 10 days thereafter duri ng which time the mice were again challenged with the same inoculum on alternate days (days +1, +3, +5, +7, and +9). Sixty-four days later, the presence of bacteria in the blood and the number of viable bacteri a in liver, spleen and appendix were estimated. Treatment with azithro mycin and 60 mg/kg/day rifabutin but not 30 mg/kg/day, significantly d ecreased the incidence of bacteraemia and the number of bacteria in th e appendix. The administration of azithromycin resulted in significant ly fewer MAC in the liver and spleen but not in the appendix whereas t he converse was true of 60 mg/kg rifabutin. Our results indicate that both azithromycin and rifabutin can prevent MAC disseminated infection , but that the azalide is more effective than the rifamycin in reducin g the burden of infection.