Disposition kinetics and in vitro plasma protein binding of cefpirome in cattle.

The disposition of cefpirome after single intramuscular (i.m.) administration (10 mg.kg-1) was investigated in five male cross-bred calves and in vitro plasma protein binding was determined. The concentration of cefpirome in the plasma was estimated by the microbiological assay technique. Binding of cefpirome to plasma proteins was determined at different concentration levels by the equilibrium dialysis technique. The peak plasma level of cefpirome after i.m. administration to cattle was attained at 45 min post-dose and the drug was detected in plasma above MIC of 0.5 μg.mL-1 for up to 10 h. The drug disposition followed a one-compartment open model. The values of t t and AUC were 0.21 ± 0.01 h, 2.06 ± 0.02 h and 31.7 ± 0.95 μg.mL 1/2Ka, 1/2β-1.h, respectively. Cefpirome was bound to the plasma proteins to the extent of 26.0 ± 2.84 percent at the concentration range of 1-100 μg.mL-1. The binding capacity of cefpirome to plasma proteins and the dissociation rate constant of the protein-drug complex were 3.71 ×10-8 ± 0.31 ×10-8 mole.g-1 and 3.43 ×10-7 ± 0.46 ×10-7 mole, respectively. Key words: calves, cefpirome, disposition, protein binding