Coagulation effects of low molecular weight heparin compared with heparin in dogs considered to be at risk for clinically significant venous thrombosis


  • North Carolina State University Veterinary Teaching Hospital, Department of Clinical Sciences Disseminated Research Grant.

Address correspondence and reprint requests to Kielyn C. Scott, Veterinary Emergency and Specialty Center of New Mexico, 4000 Montgomery Boulevard Northeast, Albuquerque, NM 87109, USA. E-mail:


Objective – Compare the effects of 3 anticoagulation protocols on anti-factor Xa activity (AXa).

Design – Prospective, randomized, double-blind study.

Setting – University veterinary teaching hospital.

Animals – Eighteen dogs considered to be at risk for venous thrombosis.

Interventions – Each dog was randomly assigned to 1 of the following 3 groups (n=6/group) and was treated for 24 hours: low-dose heparin (LDH), high-dose heparin (HDH), and dalteparin (DP). Dogs in the LDH group received a constant rate infusion (CRI) of unfractionated heparin (UFH) at 300 U/kg/d, the HDH group received a bolus of 100 U/kg of UFH IV, then a CRI of 900 U/kg/day, and the DP group received 100 U/kg DP SC at 0, 12, and 24 hours.

Measurements and Main Results – A total of 54 samples for activated partial thromboplastin time (aPTT) and AXa assays were collected at 0, 4, and 28 hours. Six samples had an AXa >0.1 U/mL, 5 of those were from the HDH group at hour 4. Two samples from the HDH group at hour 4 had a prolonged aPTT (93 and 200 seconds) and the highest AXa (0.6 and 1.0 U/mL, respectively). Four additional dogs in the HDH group did not complete the study due to hemorrhage; none of the dogs completing the study showed signs of hemorrhage.

Conclusions: Neither DP nor LDH increased AXa to values considered therapeutic in humans (0.5–1 and 0.35–0.75 U/mL, respectively), and both protocols appear to be inadequate to increase AXa in dogs with clinical illness. HDH increased AXa to this range in 2 of 6 dogs, but had unpredictable effects on aPTT and resulted in hemorrhage in some dogs.