INADEQUATE AZITHROMYCIN ACTIVITY AGAINST BRUCELLA-MELITENSIS IN MICE WITH ACUTE OR CHRONIC INFECTIONS

The activities of therapeutic regimens with azithromycin (AZI) and dox ycycline combined with streptomycin (DOX-SM) were compared in Brucella melitensis infected mice. In a chronic model, AZI given over 10, 14 o r 21 consecutive days (50 mg/kg/24 h) significantly reduced the infect ion (1.3-1.6 logs, day 48 post-infection). However, the effectiveness of DOX (21 days, 50 mg/kg/12 h) was higher than AZI (3.4 logs of reduc tion, day 48 post-infection). Besides, when DOX was administered for 4 5 days, it ''cured'' all the animals from day 78. Similar results were obtained in an acute model infection. One single dose of DOX or DOX-S M, starting one day after lethal challenge, was able to protect 83% of the mice. In contrast, only 25% of the mice treated with AZI (50-200 mg/Kg) survived the challenge. Our findings demonstrate that AZI, in c ontrast to DOX-SM, does not cure experimental brucellosis.