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Objective—To determine effects of SC administration of repeated doses of a low molecular weight heparin (LMWH) in dogs.
Animals—5 healthy dogs.
Procedure—Each dog received 6 injections (each injection, 150 U of anti-factor-Xa [anti-FXa]/kg of body weight, SC) at 8-hour intervals. Blood samples were collected before and 2 hours after the first, second, third, and sixth injections to measure heparin activity, thrombin time, activated partial thromboplastin time (APTT), antithrombin activity, Hct, and platelet count.
Results—Heparin activity varied between 0.36 ± 0.10 and 0.77 ± 0.08 U of anti-FXa/ml (before and 2 hours after the third injection) and between 0.46 ± 0.11 and 0.82 ± 0.15 U of anti-FXa/ml (before and 2 hours after the sixth injection). Thrombin time and APTT were influenced only slightly. Platelet count, Hct, and antithrombin activity started to decrease significantly 2 hours after the second LMWH injection. Because of the increased consumption of antithrombin, antithrombin activity continuously decreased from 102.1 ± 6.3% before the study to 91.0 ± 3.0% at the end of the study.
Conclusion and Clinical Relevance—Heparin plasma activity was only slightly higher than that recommended for LMWH treatment of humans, and none of the dogs had signs of increased bleeding. Thus, administration of heparin in accordance with this dosing regimen can be recommended for use in clinical studies. The screening tests investigated were not suitable for use in monitoring LMWH treatment of dogs. Assays that use chromogenic substrates are necessary to reliably monitor LMWH plasma concentrations in dogs. (Am J Vet Res 2001;62:595–598)
Objective—To evaluate SC administration of unfractionated heparin (UFH) in accordance with a dosing regimen for high-dose treatment in dogs.
Animals—10 healthy adult Beagles.
Procedures—Two groups of dogs (5 dogs/group) were given 6 injections of heparin (500 units of UFH/kg of body weight, SC) at intervals of 8 (experiment 1) and 12 (experiment 2) hours. Blood samples were collected before and 4 hours after heparin injections to determine amidolytic heparin activity, activated partial thromboplastin time (APTT), thrombin time, antithrombin activity, platelet count, and Hct.
Results—For experiments 1 and 2, mean ± SD heparin activities before (experiment 1, 1.32 ± 0.20 U/ml; experiment 2, 0.69 ± 0.174 U/ml) and 4 hours after the last heparin injection (experiment 1, 1.71 ± 0.30 U/ml; experiment 2, 1.10 ± 0.30 U/ml) were higher than values calculated for the regimen used in experiment 1. Results of the investigated thrombin time test system with low thrombin activity were frequently beyond the measurement range, even with UFH activities ≥ 0.6 U/ml. Moreover, a severe decrease of antithrombin activity became evident during both experiments (eg, in experiment 2 from 95.6 ± 4.8 to 59.2 ± 6.6%). In each treatment group, 2 dogs developed hematomas.
Conclusions and Clinical Relevance—Calculations of the course of heparin activity after a single injection do not result in a reliable dosing regimen for highdose heparin treatment in dogs. High-dose treatment must be monitored for each dog. Thrombin time measured with low thrombin activity is unsuitable for this purpose. (Am J Vet Res 2001;62:1887–1891)