Anticoagulation - oral
Exam Tips
- In OSCEs, always state both stroke/VTE risk reduction and bleeding-risk mitigation (renal function, interactions, counselling) when justifying oral anticoagulants.
- High-yield contraindication recall: DOACs are generally avoided in mechanical prosthetic valves and antiphospholipid syndrome.
- Memorise apixaban core regimens: AF 5 mg BD (reduced to 2.5 mg BD with criteria), acute VTE 10 mg BD for 7 days then 5 mg BD, extended prevention 2.5 mg BD.
- Warfarin exam phrase: delayed onset, INR-guided dosing, extensive interactions, and specific role in mechanical valve anticoagulation.
- If asked about safety, mention MHRA-style cautions: renal dose adjustment, bleeding warning signs, and availability of reversal agents.
Definition
Oral anticoagulation is the long-term use of vitamin K antagonists or direct oral anticoagulants (DOACs) to reduce formation and propagation of fibrin-rich thrombus, especially in venous thromboembolism and cardioembolic stroke risk from atrial fibrillation. In UK practice, treatment choice is indication-specific and balances thromboembolic risk against bleeding risk, with dose adjustment by renal function, age, body weight, and interacting medicines.
Pathophysiology
Anticoagulants mainly prevent fibrin-driven clot extension in lower-flow venous or cardiac stasis states rather than platelet-dominant arterial thrombosis. Warfarin reduces hepatic synthesis of vitamin K-dependent factors II, VII, IX and X (and proteins C/S), so onset is delayed (typically 48-72 hours) and INR monitoring is required. DOACs act directly: apixaban, rivaroxaban and edoxaban inhibit factor Xa, while dabigatran inhibits thrombin (factor IIa), reducing thrombin generation and fibrin clot formation. See coagulation-cascade figures in standard UK core texts (for example haemostasis diagrams in Kumar & Clark or Davidson) to link drug targets to exam mechanisms.
Risk Factors
- Non-valvular atrial fibrillation with stroke risk factors (previous stroke/TIA, age >=75 years, hypertension, diabetes, symptomatic heart failure)
- Previous or current DVT/PE, including persistent recurrence risk
- Recent major orthopaedic surgery (elective total hip or knee replacement) requiring VTE prophylaxis
- Mechanical/prosthetic valve or rheumatic valvular disease (typically warfarin rather than DOACs)
- Immobility, trauma, surgery, active cancer, pregnancy/postpartum and thrombophilia as background VTE-risk contexts
- Bleeding-risk modifiers before prescribing: renal impairment, hepatic disease, prior GI bleed/ulcer, concomitant NSAID/antiplatelet use, advanced age, low body weight
Clinical Features
Symptoms
- Often asymptomatic if anticoagulation is prescribed for AF stroke prevention
- Index VTE symptoms: unilateral leg pain/swelling, pleuritic chest pain, dyspnoea, haemoptysis
- Bleeding symptoms on treatment: epistaxis, gum bleeding, easy bruising, haematuria, melaena, heavy menstrual bleeding, headache (possible intracranial bleed)
Signs
- AF signs: irregularly irregular pulse, variable first heart sound
- DVT signs: unilateral calf swelling, tenderness, pitting oedema
- PE signs: tachycardia, tachypnoea, hypoxia, pleural rub
- Anticoagulant toxicity signs: pallor, postural hypotension, overt bleeding, neurological deficit suggesting intracranial haemorrhage
Investigations
Management
Lifestyle Modifications
- Shared decision-making on thrombosis-vs-bleeding risk and expected treatment duration
- Bleeding safety-net advice: seek urgent care for head injury, persistent bleeding, melaena, haematemesis, sudden severe headache or focal neurology
- Avoid high-risk OTC drugs that increase bleeding (especially NSAIDs) unless specifically advised
- Optimise adherence (once- or twice-daily regimen counselling), medicine reconciliation, and anticoagulant alert card use
- For warfarin: consistent dietary vitamin K intake and awareness of alcohol/drug interactions
Pharmacological Treatment
Direct oral anticoagulant (factor Xa inhibitor) - apixaban
- Apixaban 5 mg twice daily for NVAF stroke/systemic embolism prevention
- Apixaban 2.5 mg twice daily in NVAF if at least 2 of: age >=80 years, weight <=60 kg, serum creatinine >=133 micromol/L, or if CrCl 15-29 mL/min
- Apixaban 10 mg twice daily for 7 days then 5 mg twice daily for DVT/PE treatment
- Apixaban 2.5 mg twice daily for extended prevention after at least 6 months treatment
- Apixaban 2.5 mg twice daily started 12-24 h post-op for VTE prophylaxis: 32-38 days after hip replacement, 10-14 days after knee replacement
Contraindications include active clinically significant bleeding, CrCl <15 mL/min, hepatic disease with coagulopathy, antiphospholipid syndrome, prosthetic heart valve, and concomitant full-dose anticoagulant use (except while switching). Use caution with elderly patients, low body weight, renal/hepatic impairment, and concomitant NSAIDs/antiplatelets.
Other DOAC options (indication-dependent, check latest BNF/SPC)
- Rivaroxaban (e. g. NVAF usually 20 mg once daily with food; VTE treatment usually 15 mg twice daily for 21 days then 20 mg once daily)
- Edoxaban (usually 60 mg once daily; reduce to 30 mg once daily with renal impairment/low body weight/specific interactions)
- Dabigatran (commonly 150 mg twice daily for NVAF; lower-dose regimens in older or high-bleeding-risk patients)
Dabigatran and edoxaban require initial parenteral anticoagulation before starting for acute DVT/PE treatment. Avoid DOACs in antiphospholipid syndrome and mechanical valves. Review renal function at baseline and periodically.
Vitamin K antagonist
- Warfarin oral, dose titrated to INR target (no fixed dose)
Preferred in mechanical prosthetic valves and some valvular indications. Requires regular INR monitoring, interaction checks (many medicines/herbals/alcohol), and counselling about delayed onset and bleeding risk.
Reversal and bleeding management
- Warfarin reversal: vitamin K (phytomenadione), plus prothrombin complex concentrate for major bleeding
- Dabigatran reversal: idarucizumab
- Factor Xa inhibitor reversal: andexanet alfa where indicated/available, or PCC per local protocol
Major bleeding requires urgent senior/specialist input, haemodynamic support, source control, and temporary cessation of anticoagulant.
Complications
- Major bleeding including gastrointestinal haemorrhage and intracranial haemorrhage
- Clinically relevant non-major bleeding causing treatment interruption
- Thromboembolic recurrence from underdosing, poor adherence, missed doses, or inappropriate interruption
- Drug interactions leading to over- or under-anticoagulation (especially warfarin)
- Rare warfarin-specific complications (for example skin necrosis) and anticoagulant-associated nephropathy
Prognosis
When indication is correct and monitoring/adherence are good, oral anticoagulation substantially lowers stroke and recurrent VTE risk and improves long-term outcomes. Prognosis worsens with frailty, renal/hepatic dysfunction, interacting drugs, and prior major bleeding, so periodic reassessment of benefit-risk balance is essential.
Sources & References
💊BNF Drug References(1)
- Dipyridamole[management.pharmacological]
✅NICE Guidelines(1)
- Anticoagulation - oral[overview]
📖Textbook References(3)
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 462)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1421)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 463)[context]