Pharmacokinetics and Efficacy of Tilmicosin in the Treatment of <i>Pasteurella haemolytica</i> Bronchopneumonia in Calves

Abstract

Tilmicosin was administered intravenously and subcutaneously at a dose rate of 10 mg/kg bwt to determine its concentration in blood and bronchial secretion as well as its kinetic behavior in healthy and Pasteurella haemolytica type A1-infected calves. Sever acute bronchopneumonia was induced in 10 calves by inoculating them intra-tracheally with P. haemolytica type A1. The calves were treated with tilmicosin; 5 of these received the drug intravenously and the other 5 were injected subcutaneously. After a slow intravenous injection, the serum concentration-time curve indicated a two compartment open model with a mean elimination half-lives (t 1/2 b s) of 22.09 and 22.14 hours before and after infection, respectively. The mean residence time (MRT) corrected for a bolus injection was 2.25 and 2.20 hours and the mean MRT inf was 25.27 and 25.46 hours in healthy and P. haemolytica -infected calves, respectively. After subcutaneous injection, the drug was eliminated more slowly (before and after infection) from serum and bronchial secretions, with t 1/2 b s of (24.60 and 25.85 hours) and (33.74 and 31.78 hours), respectively. The apparent volume of distribution (V d(area) ) of tilmicosin was more than 1 litre · kg -1 . The peak serum and bronchial secretions of tilmicosin concentration were (1.33 and 1.36 m g · ml -1 ) and (1.40 and 1.70 m g · ml -1 ) attained at (7.21 and 7.15 hours) and 7.11 and 7.10 hours) after subcutaneous injection, respectively. Tilmicosin was good secreted into bronchial secretions having AUC bronchial secretion / AUC serum ratio of approximately 1:1.24 and 1:1.22 in healthy and P. haemolytica-