In vivo efficacies of amoxicillin and cefuroxime against penicillin-resistant Streptococcus pneumoniae in a gerbil model of acute otitis media.

The comparative efficacies of amoxicillin and cefuroxime against acute otitis media caused by a penicillin-resistant (MIC, 2 micrograms/ml) Streptococcus pneumoniae strain were assessed in a gerbil model by challenging each ear with 10(7) bacteria through transbullar instillation. Each antibiotic was tested at two doses (5 and 20 mg/kg of body weight) administered at 2, 10, and 18 h postinoculation. Samples were obtained from the middle ear (ME) on days 3 and 7 postinoculation for determination of bacterial counts. Only amoxicillin, at both doses, was able to significantly halt the weight loss in animals, reducing both the number of culture-positive animals and the bacterial concentration in ME samples versus the values for untreated animals. Comparison of the efficacies between the antibiotics, determined by their ability to achieve culture-negative ME specimens, showed that amoxicillin at 5 mg/kg was significantly more active than cefuroxime at the same dose. The use of higher doses of either amoxicillin or cefuroxime did not produce significantly better results than those obtained with the lower dose but caused a greater inflammatory response. The more favorable results obtained with amoxicillin compared with those obtained with cefuroxime could be related to the antimicrobial susceptibility of the pneumococcal strain (MICs and minimum bactericidal concentrations of 1 and 1 microgram/ml and 4 and 4 micrograms/ml for amoxicillin and cefuroxime, respectively) as well as to the better pharmacokinetic parameters obtained with amoxicillin.