Despite years of study into the best way to manage patients with immune-mediated hemolytic anemia (IMHA), articles published
as recently as 2011 still document mortality rates of 30% to 40%. In her discussion "Thromboprophylaxis in immune-mediated
hemolytic anemia," Sarah Helmond, BVSc, DACVIM, discussed the potential role of thromboprophylaxis (clot prevention strategies)
in the management of these cases.
The need for routine thromboprophylaxis is unclear, but Dr. Helmond cited several studies in which its use was associated
with higher survival rates in patients with IMHA. However, no routine classification for IMHA severity was used in those studies,
and in some instances the number of patients treated was low, making comparisons difficult.
Dr. Helmond noted two clinical trials under way to evaluate the use of thromboprophylaxis in dogs with IMHA. Ontario Veterinary
College is conducting a blinded clinical trial comparing enoxaparin to aspirin and clopidogrel, and the University of Minnesota
is conducting a randomized blinded clinical trial comparing individually adjusted unfractionated heparin and aspirin.
THROMBOPROPHYLAXIS AGENT OPTIONS
Aspirin works as a nonselective platelet inhibitor. The standard dose is 0.5 mg/kg/day, but studies assessing its efficacy
in decreasing clot formation in hypercoagulable patients have shown variable results.
Clopidogrel (Plavix—Bristol-Myers Squibb/Sanofi Pharmaceuticals) inhibits ADP-dependent platelet aggregation. Dr. Helmond
said that despite its burgeoning popularity in veterinary medicine, there is little scientific evidence to support its use
in our patients. Other inhibitors such as ticlopidine and prasugrel are being studied and may provide more efficient and safer
thromboprophylaxis options in the future.
Effective dosing and monitoring make the use of unfractionated heparin in veterinary medicine challenging, according to Dr.
Helmond. Monitoring dogs with activated partial thromboplastin times may not provide an accurate picture of coagulation status;
however, more reliable testing for anti-factor Xa concentrations is cost-prohibitive and of limited availability. The use
of thromboelastrography for monitoring patients treated with unfractionated heparin still requires further evaluation.
Low-molecular-weight heparin drugs, such as enoxaparin and dalteparin, have been found to be less predictable in dogs than
in people. Recent studies have shown promising results using enoxaparin as thromboprophylaxis in dogs with IMHA, but larger
studies are needed before this can be routinely recommended. The ideal dose and monitoring parameters still need to be elucidated.
As in people treated with low-molecular-weight heparin, hemorrhage is a potential concern when using these drugs.
1. Helmond S. Thromboprophylaxis in immune-mediated hemolytic anemia. Presented at the Annual Meeting of the American College
of Veterinary Internal Medicine; June 2012.
This "Lecture Link" summary from the 2012 American College of Veterinary Internal Medicine Forum was contributed by Jennifer
L. Garcia, DVM, DACVIM, a veterinary internal medicine specialist at Sugarland Veterinary Specialists in Houston, Texas.
Dr. Jennifer L. Garcia