Drugs

 

There are a variety of drugs that affect all aspects of hemostasis; common ones will be mentioned in more detail below. This is no means an exhaustive list.

Primary hemostasis

  • Drugs associated with thrombocytopenia: Heparin, antineoplastic agents, gold compounds, propylthiouracil (an antithyroid drug), sulfonamides, and penicillin.
  • Drugs for inhibition of platelet function: Aspirin, dazoxiben, dipyrimadole, ticlopidine and the newer GPIIb/IIIa antagonists.
  • Drugs with decreased platelet function as a side-effect: Phenothiazines, dextran, caffeine, aminophylline, antibiotics (cephalosporins, penicillin), antihistamines and barbiturates.

Secondary hemostasis

  • Drugs for therapeutic inhibition of coagulation factors: Heparin, hirudin (a specific thrombin antagonist) and warfarin. Topical anticoagulants include topical thrombin and “fibrin glue” (a mixture of cryoprecipitate, thrombin and calcium).
  • Drugs with inhibition of coagulation factors as a side effect: Polysulfated glycosaminoglycans and sulfaquinoxolone (a direct vitamin K antagonist).

Tertiary hemostasis

  • Drugs for enhancement of fibrinolysis: These are also used in human medicine to treat people with heart attacks. They include streptokinase, staphylokinase, urokinase and tissue plasminogen activator.
  • Drugs for inhibition of fibrinolysis: Aprotonin, tranexamic acid and epsilonaminocaproic acid.

Specific drugs

Aspirin

Acetylsalicylic acid is a non-steroidal anti-inflammatory drug that irreversibly acetylates platelet cyclo-oxgenase (inhibiting prostaglandin and thromboxane production) and affects platelets for the duration of their lifespan. Aspirin should not be used as an analgesic for dogs with inherited hemostatic disorders, as the effect of the drug persists even after the drug has been withdrawn (for 7 to 10 days). Aspirin can be used to prevent platelet aggregation in dogs predisposed to thrombosis, as long as the thrombosis is due to platelet hyperaggregability.

Heparin

Heparin acts primarily by potentiating the antithrombotic activity of antithrombin, but also enhances the antithrombin effects of heparin cofactor II. Heparin binds antithrombin, changing its conformation which accelerates its inhibitory activity. High molecular weight heparin fragments have little affinity for antithrombin and minimal inhibition of factor Xa, however they produce severe side-effects of hemorrhage. Low molecular weight heparin fragments have a high affinity for antithrombin, inhibit factor Xa and have minimal side-effects. Thus, they are preferred for use in thrombotic conditions.

Further information on heparin therapy is available from the Comparative Coagulation Laboratory of the Animal Health Diagnostic Center of Cornell University.

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