In vitro study of the combination of rifampin with oxacillin against Staphylococcus aureus

The rapid emergence of strains resistant to rifampin suggests that for the treatment of bacterial infections rifampin should probably be combined with another antistaphylococcal drug. The authors examine the interaction of rifampin and oxacillin in various concentrations in vitro using a dynamic biophotometric technique. While synergism was observed occasionally, most concentrations studied exhibited either antagonism or indifference. No antagonism was observed with rifampin-resistant strains. Rifampin-resistant strains often emerged when the drug was tested alone. These findings again illustrate the complex and often unpredictable effect of combining rifampin with beta-lactam antibiotics.