Pharmacodynamics of multi-dose low molecular weight heparin in healthy horses.

Objectives To compare the pharmacodynamics of once daily and twice daily administration of low molecular weight heparin (LMWH) administration in horses. Study Design Randomized cross over study. Animals Adult mixed breed healthy mares (n=6). Methods LMWH (dalteparin) was administered (50U/kg subcutaneously) either every 12 or 24hours for 3 consecutive days. Anti-factor Xa activity was measured before and at select time points after LMWH administration. Packed cell volume (PCV), platelet count, partial thromboplastin time (PTT), and anti-thrombin (AT) activity were monitored throughout the study. Results No changes in PCV, platelet count, or AT activity were detected with either frequency of daily LMWH administration. Values for PTT increased throughout the study but never exceeded the normal reference interval. Anti-factor Xa activity was maintained within or above the suggested thromboprophylactic range (0.10.2U/mL) when LMWH was administered twice daily, but fell below this range approximate to 16hours after administration when given once daily. For both once and twice daily LMWH administration, the area under the curve was significantly greater after the last dose of LMWH when compared to the first dose. Conclusions Administration of LMWH once or twice daily for 3 consecutive days appears to be safe in healthy adult horses. Anti-factor Xa activity was maintained within or above the suggested thromboprophylactic range for 24hours with twice daily LMWH administration but not with once daily administration.