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

Two field efficacy studies, involving a total of 92 naturally infected, pneumonic veal calves, were conducted to compare the efficacy of the β-lactamase inhibitor sulbactam plus ampicillin to ampicillin alone in the treatment of bacterial pneumonia. Cultures from nasal swabs and lung tissue during the 10 or 11 day studies were predominantly ampicillin-resistant Pasteurella multocida. Ampicillin (6.6 mg/kg) or sulbactam-ampicillin (3.3 mg/kg sulbactam + 6.6 mg/kg ampicillin) was injected intramuscularly once daily for either three days or six days. Sulbactam-ampicillin administered once daily for three or six days resulted in lower (P≤0.05) average body temperature with a concomitant clinical improvement (P≤0.05), and produced numerical advantages and/or statistical improvements over ampicillin in mortality, weight gain, and overall response of calves to treatment. The combined mortality for the two studies in the ampicillin and sulbactam-ampicillin treated groups was 43% and 14%, respectively. We concluded that sulbactam-ampicillin was superior to ampicillin in the treatment of ampicillin-resistant bacterial pneumonia in veal calves.