Efficacy of Sulbactam, a B-lactamase Inhibitor, Combined with Ampicillin in the Therapy of Ampicillin-resistant Pneumonic Pasteurellosis in Feedlot Calves.

Two field efficacy studies, involving a total of 80 naturally infected feedlot calves, were conducted to compare the efficacy of sulbactam-ampicillin with that of penicillin-dihydrostreptomycin in the treatment of pneumonic pasteurellosis. Cultures from pretreatment nasal swabs were predominantly ampicillin/ penicillin resistant Pasteurella haemolytica. Clinical observations revealed that cattle treated with penicillin-dihydrostreptomycin responded poorly, whereas those treated with sulbactam-ampicillin responded promptly. Twenty-four hours after initiation of treatment, mean body temperatures of the calves in the sulbactam-ampicillin groups had decreased by 2.1 degrees C, whereas, in the penicillin-dihydrostreptomycin calves there was little change. The difference between the two treatments was statistically significant (P</=0.01). The combined mortality for the two studies in the penicillin-dihydrostreptomycin treated groups was 18%. No mortality occurred in the sulbactam-ampicillin treated groups. Our data show that sulbactam-ampicillin was more effective than penicillin-dihydrostreptomycin in the treatment of pneumonia caused by ampicillin/penicillin resistant strains of Pasteurella in feedlot calves.