Effects of orally administered pimobendan on platelet function in healthy adult cats

Several phosphodiesterase inhibitors have demonstrable antiplatelet actions when administered to human patients. Concentration-dependent inhibition of feline platelet aggregation by pimobendan has been previously demonstrated in vitro. However, there are no published reports characterizing the effect of oral pimobendan, administered at therapeutic doses, on platelet function in cats. This study aimed to evaluate the effect of orally administered pimobendan on platelet function in healthy adult cats. Cats were administered pimobendan orally at a dosage of 0.625 mg/cat (low-dose) twice daily for 1 week, followed by 1.25 mg/cat (high-dose) twice daily for 1 week. Venous blood sampling for platelet testing and plasma drug concentration occurred at baseline, 1 hour postdose on the eighth day of treatment with low-dose pimobendan, 1 hour postdose on the eighth day of treatment with high-dose pimobendan, and after a 1-week washout period. Platelet function was assessed by whole blood aggregometry and by use of a platelet function analyzer (PFA-100 (R)). Friedman tests were used to compare platelet function parameters among the 4 sampling timepoints. After 1 week of treatment, median (range) plasma pimobendan concentrations were 15.1 ng/mL (6.89-20.2 ng/mL) and 32.8 ng/mL (23.3-44.8 ng/mL) in cats receiving low-dose and high-dose pimobendan, respectively. No significant differences in PFA closure time or any aggregometry variable were found among the treatment conditions. Pimobendan was not associated with measurable inhibition of platelet function when administered orally to healthy adult cats at 2 clinically relevant dosages.