Makindo Medical Notes

Anticoagulants and antiplatelets are vital for preventing thrombosis but carry a major risk of bleeding. ✅ Indications: atrial fibrillation, DVT/PE, mechanical heart valves, MI, PCI, stroke prevention. ⚠️ Key complication: haemorrhage (minor bruising → life-threatening GI or intracranial bleed).

🧬 Mechanism of Action (Physiology)

• Anticoagulants: Act on the coagulation cascade, inhibiting clotting factor activation (extrinsic/intrinsic pathways). Prevent fibrin clot formation (e.g., warfarin, heparin, DOACs).
• Antiplatelets: Block platelet aggregation (primary haemostasis). Prevent arterial clot formation on ruptured plaques (e.g., aspirin, clopidogrel, ticagrelor).

📌 Common Anticoagulants

• Warfarin: Vitamin K antagonist (factors II, VII, IX, X). 🔎 Requires INR monitoring (target 2–3). ⚠️ Issues: drug/food interactions, teratogenicity, bleeding.
• Unfractionated Heparin (UFH): Potentiates antithrombin III → inhibits thrombin + factor Xa. 🔎 Monitor with aPTT. ⚠️ Risks: bleeding, heparin-induced thrombocytopenia (HIT).
• DOACs (Apixaban, Rivaroxaban, Dabigatran): Direct Xa or thrombin inhibitors. ✅ No routine monitoring needed. ⚠️ Consider renal clearance, drug interactions.

📊 Comparison: Anticoagulants vs Antiplatelets

Feature	Anticoagulants 💉	Antiplatelets 💊
Mechanism	Inhibit coagulation cascade (fibrin clot formation)	Inhibit platelet aggregation (primary haemostasis)
Examples	Warfarin, Heparin, DOACs (apixaban, rivaroxaban, dabigatran)	Aspirin, Clopidogrel, Ticagrelor
Main Indications	AF (stroke prevention), DVT, PE, mechanical valves	MI, stroke/TIA, post-stenting, secondary prevention in CAD
Monitoring	Warfarin → INR; UFH → aPTT; DOACs → none routine	No routine monitoring needed
Main Side Effect	Bleeding (esp. GI, intracranial); HIT with heparin	Bleeding (esp. GI), dyspepsia, allergy
Reversal	Warfarin → Vitamin K + PCC/FFP Heparin → Protamine Dabigatran → Idarucizumab Xa inhibitors → Andexanet alfa or PCC	Aspirin/Clopidogrel → Platelet transfusion (partial benefit) Ticagrelor → Limited reversal, supportive
Risk–Benefit Balance	Best for venous thrombosis and embolic stroke prevention	Best for arterial thrombosis (plaque rupture, stents)

🚨 Managing Bleeding – Anticoagulants

• Warfarin: ➡️ Minor: stop & monitor. ➡️ Moderate: oral vitamin K. ➡️ Severe/life-threatening: IV vitamin K + PCC (prothrombin complex) or FFP.
• Heparin: ➡️ Minor: stop infusion. ➡️ Moderate/severe: protamine sulfate (dose based on timing/dose of UFH/LMWH). ➡️ HIT: stop heparin, switch to non-heparin anticoagulant (argatroban, fondaparinux).
• DOACs: ➡️ Minor: stop drug & monitor renal function. ➡️ Dabigatran: idarucizumab is specific antidote. ➡️ Xa inhibitors: andexanet alfa (if available) or PCC. ➡️ Severe: supportive care + reversal agents.

💊 Common Antiplatelets

• Aspirin: Irreversible COX-1 inhibitor → ↓ thromboxane A2. Used in CAD, MI, stroke prevention. ⚠️ GI irritation, bleeding, allergy.
• Clopidogrel: Irreversible P2Y12 receptor blocker. Used post-stent, ACS, stroke/TIA prevention. ⚠️ Bleeding, dyspepsia.
• Ticagrelor: Reversible P2Y12 inhibitor. Used in ACS/PCI. ⚠️ Bleeding, dyspnoea, bradycardia.

🚨 Managing Bleeding – Antiplatelets

• Aspirin: ➡️ Minor: stop & monitor. ➡️ Severe: consider platelet transfusion + supportive care.
• Clopidogrel: ➡️ Minor: stop drug. ➡️ Severe: stop + platelet transfusion (variable benefit).
• Ticagrelor: ➡️ Severe bleed: stop + platelet transfusion (less effective due to reversible binding). ➡️ Supportive care essential.

⚖️ Balancing Risks

• ⚠️ Always weigh bleeding risk against thrombosis risk (e.g., stroke in AF, stent thrombosis post-PCI).
• 🫀 Dual antiplatelet therapy (DAPT: aspirin + clopidogrel/ticagrelor) is vital post-PCI but increases bleeding risk.
• 💊 Warfarin is still first-line in mechanical heart valves and severe renal impairment.
• ✅ DOACs are preferred in AF/VTE for ease and safety.

💡 Clinical Pearls

• 👴 Elderly, renal/hepatic impairment = ↑ bleeding risk. Adjust doses.
• 🔄 Reversal agents should be readily available in all hospitals.
• 📊 Use bleeding risk scores (HAS-BLED) and thrombotic risk scores (CHA₂DS₂-VASc) to guide decisions.
• 🧑‍⚕️ In emergencies: resuscitate first, stop anticoagulant, reverse if needed, then re-evaluate thrombotic risk.