Comparative in vitro and in vivo efficacy of roxithromycin and erythromycin against a strain of methicillin-susceptible Staphylococcus epidermidis

The in vitro and in vivo efficacy of roxithromycin was compared with that of erythromycin, against a methicillin-susceptible strain of Staphylococcus epidermidis. We performed standard in vitro testing (MIC, MBC, and time-kill kinetics) for roxithromycin, erythromycin, and rifampin. Both macrolides were bacteriostatic in vitro. There was no significant difference in microbial survival between erythromycin and roxithromycin groups in the time-kill kinetics (p = 0.3). For the in vivo experiments, using the rabbit experimental endocarditis model, roxithromycin was found to be inferior to erythromycin in decreasing the microbial burden of the endocardial vegetations (p <0.05). Rifampin was highly effective, both in vitro and in vivo. In conclusion, the efficacy of roxithromycin was poor and inferior to erythromycin against a strain of methicillin-susceptible S. epidermidis.