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Ampicillin, sulbactam, and rifampin combination treatment of experimental methicillin-resistant Staphylococcus aureus
H F Chambers1, M Kartalija, M Sande
1Medical Service, San Francisco General Hospital, CA 94143-0811.
Abstract:
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. Studies were done to determine whether the addition of rifampin would permit lowering the dose of ampicillin into the range recommended for use in humans without loss of efficacy. The efficacy of ampicillin/sulbactam (300/150 or 150/75 mg/kg/day intramuscularly, in three divided doses) in combination with rifampin (5 mg/kg intramuscularly, three times 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 endocarditis. Neither ampicillin/sulbactam nor rifampin alone was effective. The ampicillin/sulbactam/rifampin regimen was as effective as vancomycin. This regimen may be an alternative to vancomycin in treatment of methicillin-resistant S. aureus infections.
Insights
Adding rifampin to ampicillin/sulbactam demonstrated efficacy against methicillin-resistant Staphylococcus aureus (MRSA) endocarditis in rabbits, matching vancomycin effectiveness. This combination may offer an alternative treatment for MRSA infections.
Area of Science:
- Infectious Diseases
- Pharmacology
- Microbiology
Background:
- Methicillin-resistant Staphylococcus aureus (MRSA) poses a significant threat in healthcare settings.
- Vancomycin is a primary treatment for MRSA infections, but resistance is a growing concern.
- Beta-lactam antibiotics combined with beta-lactamase inhibitors show promise against MRSA in animal models.
Purpose of the Study:
- To evaluate the efficacy of ampicillin/sulbactam combined with rifampin against MRSA endocarditis in a rabbit model.
- To determine if rifampin allows for a reduced, human-relevant dose of ampicillin without compromising effectiveness.
- To compare the efficacy of this novel regimen to vancomycin.
Main Methods:
- A rabbit model of aortic valve endocarditis caused by MRSA was utilized.
- Animals were treated with ampicillin/sulbactam plus rifampin, ampicillin/sulbactam alone, rifampin alone, or vancomycin.
- Bacterial titers in cardiac vegetations and valve tissues were assessed to determine treatment efficacy.
Main Results:
- Neither ampicillin/sulbactam nor rifampin monotherapy was effective in treating MRSA endocarditis.
- The combination of ampicillin/sulbactam and rifampin demonstrated efficacy comparable to vancomycin.
- The tested regimen achieved significant bacterial reduction in cardiac vegetations.
Conclusions:
- The combination of ampicillin/sulbactam and rifampin is a potentially effective alternative to vancomycin for treating MRSA endocarditis.
- Further clinical studies are warranted to confirm the safety and efficacy of this regimen in humans.
- This combination therapy could expand treatment options for challenging MRSA infections.