Potential of clindamycin in addition to vancomycin for the treatment of oxacillin-resistant Staphylococcus aureus septicemia persisting under vancomycin therapy.

We observed seven patients with persistent fever and staphylococcemia under vancomycin-containing antimicrobial regimens who promptly improved as clindamycin was added to the initial antibiotics. Moreover, in all these patients a striking increase in peak and trough serum inhibitory activity (SIR) and serum bactericidal activity (SBA) levels was observed after addition of clindamycin. SIA and SBA levels after administration of a single dose of vancomycin (500 mg), clindamycin (600 mg) or vancomycin + clindamycin were also measured in three healthy volunteers against six ORSA isolates. Unsatisfactory peak SBA levels (0% of cases 1:8) were obtained after vancomycin administration. Vice versa, peak SBA levels 1:8 were obtained in 94% of the cases after clindamycin and in 100% of cases after vancomycin + clindamycin. Time-kill studies showed a borderline or incomplete bactericidal activity of vancomycin against three ORSA isolates from infections that manifested poor or slow response to vancomycin therapy. The combination with clindamycin did not result in a synergistic interaction between the two drugs. It is concluded that addition of clindamycin may be useful in some cases of ORSA septicemia that show poor or slow response to vancomycin therapy. The recommendation for a wider use of this combination of antibiotics requires further documentation of efficacy.