The pharmacokinetics of salicylate in dairy cattle are not altered by simultaneous intravenous ceftiofur sodium and DL-lysine-acetyl salicylate (aspirin).

This study evaluated potential alterations to the pharmacokinetics of salicylate by concurrently administered ceftiofur sodium. The trial design was a cross-over using 10 non-lactating, non-pregnant dairy cows. In the first period each cow received intravenously (i.v.) 26 mg/kg of DL-lysine acetyl salicylate (aspirin) followed immediately by 2 mg/kg ceftiofur sodium. In the second period each cow received 26 mg/kg of aspirin i.v. Plasma samples were harvested for determination of salicylate concentration by HPLC. The data best fitted a single compartment open model, using weighted non-linear regression. No alterations to the pharmacokinetic parameters of salicylate in cattle by concurrently administered ceftiofur sodium were detected (P < 0.05). Using 90% confidence intervals, and testing for changes of > 20%, control values, elimination half-life (t1/2), apparent volume of distribution (Vd), area under the plasma concentration versus time curve (AUC) and mean residence time (MRT) were not altered. For control animals the elimination rate constant (k(el)) and total body clearance (Cl) were 1.35 +/- 0.43 h-1 and 20.2 +/- 6.1 ml/h.kg respectively (mean +/- SD). Since ceftiofur sodium did not affect the pharmacokinetics of salicylate, dose regimens for aspirin in cattle need not be altered when ceftiofur sodium is administered concurrently.