Antiplatelet drugs

Aspirin

Inhibits conversion of platelet-derived arachidonic acid to thromboxane A₂, and hence thromboxane A₂–induced platelet activation and aggregation

Generally less efficacious than clopidogrel

Ideal dose to maximize benefit and minimize adverse effects is not known

Dogs: 0.5–10 mg/kg, PO, q 24 h, long-term

Cats: 81 mg/cat, PO, q 72 h, long-term

Not required, but hematocrit and renal function should be periodically monitored

Clopidogrel

Adenosine phosphate (P2Y12) receptor antagonist

Dog: 1.1–3 mg/kg, PO, q 24 h, long-term

Cats: 18.75 mg/cat, PO, q 24 h, long-term

Not required, but platelet aggregometry is useful in research settings

Anticoagulants

Rivaroxaban

Direct inhibitor of factor Xa

Dogs: 1–2 mg/kg, PO, q 24 h, long-term

Cats: 0.5–1.0 mg/kg, PO, q 24 h, long-term

Not required, but rivaroxaban's specific anti-Xa activity is useful in research settings

Dalteparin

Low-molecular-weight heparin, which binds to and potentiates the endogenous anticoagulant antithrombin, enhancing its inhibition of factor Xa

Minimal factor IIa inhibition (unlike unfractionated heparin)

Dogs: 100–175 U/kg, SC, q 8 h, as needed for antithrombotic effect

Cats: 75 U/kg, SC, q 6 h, as needed for antithrombotic effect

Not required, but titration to target anti-Xa activity has been investigated

Enoxaparin

Low-molecular-weight heparin with mechanism as for dalteparin

Dogs: 0.8 mg/kg, SC, q 6 h, as needed for antithrombotic effect

Cats: 0.75–1.0 mg/kg, SC, q 6 h, as needed for antithrombotic effect

Not required, but can consider titration to target anti-Xa activity

Unfractionated heparin

Binds to and potentiates the endogenous anticoagulant antithrombin and enhances its inhibition of several coagulation factors, particularly factors Xa and IIa (thrombin)

Dogs: 100 U/kg, IV bolus, then CRI at 480–900 U/kg/d; or 150–300 U/kg, SC, q 6 h, as needed for antithrombotic effect

Cats: Only SC route has been investigated; initial dose 250 U/kg, SC, q 6 h, as needed for antithrombotic effect

Optimal dose likely varies from case to case

Close monitoring of either activated clotting time, activated partial thromboplastin time, or anti-Xa activity is necessary, because of narrow therapeutic index, to maximize antithrombotic effect and minimize hemorrhagic complications

Thrombolytics

Tissue plasminogen activator (alteplase)

Binds to fibrin within thrombus, initiating fibrinolysis and converting plasminogen to plasmin

Dogs: Using a 250 mcg/mL injection, 25 mcg/dog, intracamerally in anterior chamber of affected eye, once (total volume must not exceed 0.1 mL)

Monitor for response to treatment and for adverse effects (eg, hyperkalemia); recommended only for hospitalized patients with intensive monitoring and 24-h observation