IN-VITRO AND IN-VIVO ACTIVITIES OF AZITHROMYCIN, A NEW AZALIDE ANTIBIOTIC, AGAINST CHLAMYDIA

The in vitro and in vivo activities of azithromycin against chlamydia were investigated. The MIC of azithromycin for five standard strains o f different species of chlamydia and six wild type strains of Chlamydi a pneumoniae was 0.125 mu g/ml, which was superior to that of erythrom ycin but inferior to those of clarithromycin and minocycline. However, the therapeutic effect of a 7-day course of azithromycin at a dose of 10 mg/kg of body weight administered orally once daily to mice with e xperimental Chlamydia psittaci pneumonia was excellent, with a 100% su rvival rate at 14 days after infection, which was the same as that for treatment with minocycline administered at 10 mg/kg twice daily; all erythromycin treated animals died within 10 days. When treatment was d iscontinued 3 days after the infection, the survival rate for mice tre ated with azithromycin was 90% and that for mice administered minocycl ine was 30%. These results suggest that azithromycin may be useful in the treatment of respiratory infections caused by intracellular pathog ens, including chlamydia because of its excellent accumulation within host cells.