Imipenem-cilastatin in the treatment of methicillin-sensitive and methicillin-resistant Staphylococcus aureus infections

Imipenem-cilastatin was evaluated for efficacy and toxicity as an antistaphylococcal agent in 23 patients; 11 of these patients were infected with methicillin-resistant Staphylococcus aureus (MRSA), and 12 were infected with methicillin-susceptible S. aureus (MSSA). There were 15 soft tissue, 5 endovascular, and 3 skeletal infections and a total of nine patients with bacteremia. As determined by in vitro susceptibility testing, the MICs for 90% of the MRSA and MSSA isolates tested were 6.25 and 0.39 micrograms/ml, respectively. Two MRSA isolates were resistant to a concentration of greater than 16 micrograms/ml. When 11 MRSA isolates and 7 MSSA isolates were incubated for 48 h the MICs for 90% of the isolates increased to greater than 50 micrograms/ml for the MRSA isolates and 6.25 micrograms/ml for the MSSA isolates. Three S. aureus isolates emerged resistant. Ten of 11 (91%) MRSA infections and 11 of 12 (92%) MSSA infections were clinically cured. Adverse reactions occurred in 25% of the imipenemcilastatin-treated patients. These reactions included gastrointestinal intolerance (7% of the patients), rash or pruritus (6%), eosinophilia (6%), thrombocytosis (4%), and a positive, direct Coomb test without hemolysis (3%). One of the two patients for whom therapy was discontinued because of gastrointestinal intolerance had antibiotic-associated colitis. Imipenem appears to be an effective antistaphylococcal agent against both MRSA and MSSA infections.