Clopidogrel
**Clopidogrel** is a potent oral platelet aggregation inhibitor (thienopyridine class) widely used in veterinary medicine to prevent dangerous blood clots (thromboembolism). - **Feline Medicine**: It is frequently used to prevent **Feline Aortic Thromboembolism (FATE)** in cats with underlying heart disease (e.g., Hypertrophic Cardiomyopathy). It may also improve pelvic limb circulation after an embolic event via vasomodulating effects. - **Canine Medicine**: Used to manage hypercoagulable states associated with conditions like **Immune-Mediated Hemolytic Anemia (IMHA)**, Protein-Losing Enteropathy/Nephropathy (PLE/PLN), and hyperadrenocorticism. **Clinical Pearl**: Clopidogrel is notoriously bitter. Cats may hypersalivate profusely if they taste the tablet. Placing the dose inside an empty gelatin capsule is highly recommended to ensure compliance.
Mechanism: Clopidogrel is a **prodrug** that requires hepatic biotransformation (via **CYP450** enzymes) to its active, highly unstable thiol metabolite. - The active metabolite → binds selectively and **irreversibly** to the **P2Y12** subtype of **ADP-receptors** on the platelet surface. - This blocks **ADP** binding → prevents activation of the **glycoprotein IIb/IIIa** complex. - Without this complex, platelet-fibrinogen binding cannot occur, effectively halting both primary and secondary platelet aggregation. - It also inhibits the release of other pro-aggregation compounds (serotonin, calcium, thromobospondin). Because the binding is irreversible, the platelet is inhibited for its entire lifespan (approximately 7-10 days). Normal coagulation only returns as new platelets are synthesized.
Dosing by species
- As an anti-platelet agent · 1-3 mg/kg PO once daily; if used with aspirin give lower doses (0.5-1 mg/kg PO once daily) · PO · once daily
- Thromboprophylaxis · 1.1-4 mg/kg · PO · q24h · A single loading dose of 4-10 mg/kg p.o. may help achieve therapeutic concentrations more rapidly.
- To prevent thrombus formation · 18.75 mg (practically, 1/4 of a 75 mg tablet) PO once daily · PO · once daily
- To prevent thrombus formation (combination therapy) · 7 mg (total dose) PO once daily in combination with aspirin 40-81 mg (total dose) every 3 days. · PO · once daily · Clinical trials are needed to determine appropriate dosage and indications.
- To prevent thrombus formation · 1-3 mg/kg PO once daily; if used with aspirin give lower doses (0.5-1 mg/kg PO once daily) · PO · once daily
- Thromboprophylaxis · 18.75 mg/cat · PO · q24h · A single loading dose of 4-10 mg/kg p.o. may help achieve therapeutic concentrations more rapidly. Administer in a gelatin capsule to improve compliance due to bitter taste.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Routes of administration
Contraindications
- Active pathologic bleeding
- Known hypersensitivity to the drug
Adverse effects
- Vomiting
- Anorexia
- Bleeding/hemorrhage
- Diarrhea
- Rashes
- Thrombotic thrombocytopenic purpura (TTP) - rare in humans
Drug interactions
- Aspirin · Increased risk for bleeding; however, many patients take both medications intentionally for dual antiplatelet therapy. · moderate
- Heparin / Low Molecular Weight Heparins (LMWH) · Clopidogrel appears safe to use concurrently with heparin.
- NSAIDs · Increased risk for bleeding; clopidogrel may interfere with NSAID metabolism.
- Phenytoin · Clopidogrel may interfere with phenytoin metabolism.
- Proton Pump Inhibitors (e.g., omeprazole) · May decrease the efficacy of clopidogrel by inhibiting CYP2C19, the enzyme needed to convert clopidogrel to its active metabolite.
- Torsemide · Clopidogrel may interfere with torsemide metabolism.
- Warfarin · Increased risk for bleeding; clopidogrel may interfere with warfarin metabolism.
- Anticoagulants · High risk of bleeding complications · major
Monitoring
- Clinical efficacy (prevention of thromboembolic events)
- Adverse effects (vomiting, anorexia)
- Signs of bleeding (petechiae, ecchymosis, melena, epistaxis)
Overdose
Limited information is available. Reported lethal oral doses for mice and rats were 1500 mg/kg and 2000 mg/kg, respectively. **Clinical Signs**: Acute toxic signs may include bleeding or vomiting. **Treatment**: Platelet transfusions have been suggested if rapid reversal is required.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.