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)