AMPICILLIN, SULBACTAM, AND RIFAMPIN COMBINATION TREATMENT OF EXPERIMENTAL METHICILLIN-RESISTANT STAPHYLOCOCCUS-AUREUS ENDOCARDITIS IN RABBITS

Ampicillin or amoxicillin at 625-800 mg/kg/day, in combination with a beta-lactamase inhibitor, each is as effective as vancomycin in animal models of methicillin-resistant Staphylococcus aureus endocarditis. S tudies were done to determine whether the addition of rifampin would p ermit lowering the dose of ampicillin into the range recommended for u se in humans without loss of efficacy. The efficacy of ampicillin/sulb actam (300/150 or 150/75 mg/kg/day intramuscularly, in three divided d oses) in combination with rifampin (5 mg/kg intramuscularly, three tim es daily) was compared with that of vancomycin (25 mg/kg intravenously , twice daily, or 30 mg/kg intramuscularly, three times daily) in the rabbit model of methicillin-resistant S. aureus aortic valve endocardi tis. Neither ampicillin/sulbactam nor rifampin alone was effective. Th e ampicillin/sulbactam/rifampin regimen was as effective as vancomycin . This regimen may be an alternative to vancomycin in treatment of met hicillin-resistant S. aureus infections.