Comparative in vitro activities of clarithromycin, azithromycin, and erythromycin against Borrelia burgdorferi

The in vitro activities of the macrolide antibiotics clarithromycin, 14- hydroxy-clarithromycin, azithromycin, and erythromycin against 19 isolates of Borrelia burgdorferi were investigated. MICs ranged from 0.003 to 0.03 μg of clarithromycin per ml, 0.007 to 0.03 μg of 14-hydroxyclarithromycin per ml, 0.003 to 0.03 μg of azithromycin per ml, and 0.007 to 0.06 μg of erythromycin per ml. Time-kill studies using the B31 strain of B. burgdorferi demonstrated a ≥3-log₁₀-unit killing after 72 h with each of the macrolide antibiotics tested in concentrations representing twice the respective MICs.