Comparative antimicrobial activity of the new macrolides against Borrelia burgdorferi

The in vitro and in vivo activity of the new macrolides azithromycin, clarithromycin and roxythromycin was compared with that of erythromycin against Borrelia burgdorferi. In in vitro tests using ten clinical isolates all macrolides were highly active against Borrelia burgdorferi (MIC90 0.015-0.06 micrograms/ml). Azithromycin was more potent than the other macrolides in experimental animal infection, eradicating the organism in all animals tested at a dosage of 8 mg/kg.