Abstract: Background Pimobendan is an inodilator approved for treatment of canine cardiac disease. The pharmacokinetics have not been investigated in horses.
Hypothesis/Objectives This study evaluated the pharmacokinetics of oral Vetmedinīĸ (V) in horses. Additional objectives were to determine the bioequivalence of compounded pimobendan capsules (C) and suspension (S) and the effects of sample site on plasma drug concentrations.
Animals Six privately-owned healthy adult horses (5 mares, 1 gelding).
Methods All horses received a single 0.5mg/kg dose of pimobendan via oral syringe. The initial two horses received C, S, or V using a crossover design with a minimum 1-week washout period. Samples were collected simultaneously from lateral thoracic and jugular catheters before and after drug administration at predetermined times. Differences between formulation and sample site were analyzed by one-way ANOVA. The remaining 4 horses received (V) only with jugular samples collected. Analysis was by LC-MS/MS and noncompartmental pharmacokinetics for (V).
Results No significant differences were noted between formulations or sample site (P > 0.05). Concentrations in compounded formulations were 90%(C) and 88%(S) of label. For V, mean (±SD) maximum plasma concentration (Cmax) was 4.96 ± 2.13ng/mL at 2.17 ± 0.98hr, and area under the curve (AUC0–∞) was 22.1 ± 8.8hr*ng/mL. ODMP was not detected in any sample (< 0.07ng/mL).
Conclusions and clinical importance At 0.5mg/kg PO, pimobendan plasma concentrations were considerably lower than reported in dogs. There was no evidence of oral transmucosal absorption. Pimobendan is poorly absorbed in horses, regardless of formulation, and appears unlikely to have clinical effects.
