Amdinocillin has previously been shown to be synergistic with other beta-lactam antibiotics against many gram-negative bacteria. We evaluated the safety, efficacy, and microbiologic activity of combination amdinocillin and cefoxitin treatment in 17 patients with complicated urinary tract infections caused by multiply-resistant Serratia marcescens. Patients were treated with amdinocillin, 40 mg/kg per day, and cefoxitin, 100 mg/kg per day, for five to 14 days. In vitro synergistic activity was observed for 17 isolates using broth checkerboard testing and for nine isolates using combination disc diffusion testing. Of the 17 patients treated, 11 were bacteriologically cured, one failed to respond, and five patients had a relapse after initial improvement. Relapses followed short-duration therapy. Amdinocillin with cefoxitin was well tolerated. Combination amdinocillin and cefoxitin therapy was efficacious and safe in treating complicated urinary tract infections caused by multiply-resistant S. marcescens.
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