ln-vitro effects of vancomycin, rifampicin, and fusidic acid, alone and in combination, against methicillin-resistant Staphylococcus aureus

Minimal inhibitory and minimal bactericidal concentrations were determined for eighteen methicillin-resistant Staphylococcus aureus isolates, the majority also re-sistant to gentamicin, obtained from the blood of bacteraemic patients. Fifty per cent of organisms had a greater than four-fold difference in M.I.C. and M.B.C. for vancomycin, 83 % for rifampicin, and 89 % for fusidic acid. In-vitro effects of two-drug combinations of vancomycin, rifampicin, and fusidic acid demonstrated neither synergy nor antagonism when measured by a checkerboard dilution tech-nique. The relevance of these findings to choice of therapy of serious infection due to methicillin-gentamicin resistant Stapk aureus is yet to be determined