Pharmacokinetic and Pharmacodynamic Studies of Tulathromycin in Buffalo Calves

The response of pneumonic buffalo calves to therapy with tulathromycin was evaluated in a private farm in Zagazig city, SharkiaProvince. A total number of 16 calve 3-9 months old (11clinically healthy calves and 5 pneumonic calves) were used in this investigation. Ten buffalo calves were classified into 2 equal groups each of 5 calves, 1^st group were healthy calves (control group) and 2^nd group calves were suffered from pneumonia treated with tulathromycin. Blood samples were collected for stydying the effect of tulathromycin treatment on biochemical parameters of pneumonic calves. Pharmacokinetics of tulathromycin were studied after single dose I/V, I/M and S/C injection. Six apparently healthy buffalo calves were used in a crossover design.
Pneumonic calves showed significant decrease in total proteins, albumin, globulin, and significant increase in AST, ALT, total bilirubin, glucose urea and creatinine. Ca was insignificantly decreased, meanwhile Na and K were insignificantly increased. Biochemical parameters were returned to their normal levels on 15 days post treatment.
After I/V injection of tulathromycin, half-lives of distribution and elimination (t_{0.5 (α)} and t_{0.5 (β)}), volume of distribution at steady state (Vd), and total body clearance (Cl_B) were 0.17 h., 48.35 h., 4.25 L kg^-1., and 0.06 L kg^-1 h^-1, respectively. Following I/M and S/C tulathromycin injection, maximum concentration (C_max) 0.33 and 0.31ug ml^-1 were achieved at a maximum times (t_max) 1.12 and 1.23h., respectively. The mean values for absorption and elimination half-lives (t_0.5(ab) and t_0.5(el)) and MRT were 0.14 and 0.16 h., 68.93 and 65.87 h., 99.56and 95.17h respectively. The I/M and S/C bioavailabilities were 82.8 and 71.9% respecti- vely. Result of in-vitro protein-binding study indicated that 38.9% of tulathromycin was bound to calves serum proteins.
It could be concluded that treatment by tulathromycin induce disappepearance of  the clinical signs of pneumonia in buffalo calves and biochemical parameters returned  to their normal levels.