COMPARISON OF THE EFFECTS OF LOW-MOLECULAR-WEIGHT AND UNFRACTIONED HEPARIN IN HORSES

Thirty healthy male horses were allotted to 3 groups and treated blind ly during 4 days. Group-1 horses received unfractioned calcium heparin (100 IU/kg of body weight, SC, q 12 h). Group-2 horses received a sin gle dose of a low-molecular-weight heparin (50 anti-X(a) IU/kg, SC) ev ery morning, and a similar volume of saline solution every evening. Gr oup-3 horses received the vehicle (saline solution), SC, every 12 hour s. Citrated and EDTA-anticoagulated blood samples were collected befor e starting the medication (T-0) and once daily 3 hours after each morn ing injection (T-3, T-27, T-51, and T-75). The PCV, hemoglobin concent ration, RBC and platelet counts, and clotting times (activated partial thromboplastin time and thrombin time) were determined, and a microsc opic examination to detect hemagglutination was performed. Plasma conc entration of heparin was measured by use of the antifactor X(a) activi ty assay. Bleeding time was determined on the first and fourth days, u sing a double-template method. The horses given unfractioned heparin h ad marked agglutination of erythrocytes after the first injection that became more pronounced as treatment progressed. Also, significant dec rease in PCV, hemoglobin concentration, and RBC count was observed dur ing treatment. Platelet count was significantly decreased after the fi rst day, and clotting times were significantly prolonged. In contrast to the horses given unfractioned heparin, those given low-molecular-we ight heparin did not have any agglutination of erythrocytes during the 4 days of treatment, and there were no significant changes in PCV, he moglobin concentration, or RBC and platelet counts. Activated partial thromboplastin time increased slightly in the horses given low-molecul ar-weight heparin, although the values remained within reference range . Both groups of horses achieved adequate concentrations of heparin in plasma for prophylactic purposes, but those given low-molecular-weigh t heparin achieved those values after the first injection. Bleeding ti mes were not significantly different between heparin-treated horses an d horses given saline solution during treatment. We conclude that low- molecular-weight heparin may be used more safely and conveniently in h orses, because it does not affect equine erythrocytes, platelets, or c lotting and bleeding times.