Use of Unfractionated Heparin (UH) Versus Low Molecular Weight Heparin (LMWH) in Critically Ill Dogs
C. Thorneloe; C. Bedard; S. Boysen; M. Dunn
LMWHs exert their anticoagulant activity by binding to antithrombin III and preferentially inhibiting factor X. This results in inhibition of hemostasis with minimal prolongation of PT and aPTT. These characteristics make LMWHs an interesting therapeutic alternative to UH.
The goals of this prospective randomized blinded clinical study were to 1) compare the efficacy of LMWH (dalteparin) and UH in critically ill dogs using antiXa activity and 2) demonstrate that at a fixed dosage, LMWH has a predictable effect on coagulation and does not prolong clotting times.
Dogs were assigned randomly to one of two groups. Group 1 received LMWH 150U/kg SC TID and group 2 received UH 200U/kg SC TID for 48 hours. For each dog, the following parameters were measured anti-Xa activity, PT, aPTT and ATIII on day one at baseline (T0) and at 3, 8 and 24 hours and on day two at 3 and 8 hours.
Fifteen dogs were enrolled in the study. 7 received LMWH and 8 received UH. All dogs receiving LMWH had anti-Xa activity within or above the target range (0.4-1.0U/ml) on day 1 T3 and 8. None of the dogs receiving UH had anti-Xa activity within the target range on day 1 T3 and 8. ATIII levels were similar in both groups. No prolongation in PT or aPTT was noted except for one dog in the LMWH group.
Unlike UH, LMWH yielded predictable antiXa activities in critically ill dogs, was well tolerated and in general did not result in prolonged clotting times.