Anticoagulant Prescribing for Atrial Fibrillation

Anticoagulation in atrial fibrillation prevents stroke and systemic embolism. Offer treatment to men with a CHA2DS2-VASc score of 2 or more and women with a score of 3 or more, and consider it at 1 in men and 2 in women. Direct oral anticoagulants are first choice, except in mechanical heart valves and moderate to severe mitral stenosis, where warfarin is required. Rheumatic heart disease is common in East Africa, so check for mitral stenosis by echocardiography before choosing a direct oral anticoagulant.

Bleeding risk. Assess and correct modifiable factors: uncontrolled pressure, alcohol excess, NSAIDs, unneeded antiplatelet drugs and anaemia. A high score alone does not stop treatment.

Baseline. Creatinine clearance by Cockcroft-Gault, weight, haemoglobin, platelets, liver tests and interacting drugs.

Apixaban. 5 mg orally twice daily. Reduce to 2.5 mg twice daily when two of the following apply: age 80 years or over, weight 60 kg or under, creatinine 133 micromol/L or over.

Rivaroxaban. 20 mg orally once daily with the evening meal. Use 15 mg once daily if creatinine clearance is 15 to 49 mL/min.

Dabigatran. 150 mg orally twice daily. Use 110 mg twice daily at age 80 or over, or with verapamil. Avoid if creatinine clearance is under 30 mL/min.

Edoxaban. 60 mg orally once daily. Use 30 mg once daily if creatinine clearance is 15 to 50 mL/min, weight is 60 kg or under, or with ciclosporin, dronedarone, erythromycin or ketoconazole.

Warfarin. Start 5 mg orally once daily (2 to 3 mg in older adults, liver disease, or with interacting drugs), adjust by INR to a target of 2.0 to 3.0. Check INR on days 3 to 5, then twice weekly until stable, then every 4 weeks at most. Time in range should exceed 70%.

Mechanical valves and mitral stenosis. Warfarin only. Direct oral anticoagulants are contraindicated in mechanical valves.

Special groups.

• In pregnancy, warfarin is teratogenic in weeks 6 to 12 and direct oral anticoagulants are avoided, so use enoxaparin 1 mg/kg subcutaneously twice daily.
• In breastfeeding, warfarin is compatible.
• In older adults, use the dose-reduction criteria, not age alone.
• In creatinine clearance under 15 mL/min or dialysis, specialist advice is needed.
• In hepatic impairment, avoid in Child-Pugh C.
• In HIV and tuberculosis treatment, rifampicin, ritonavir and some antiepileptic drugs interfere, so avoid direct oral anticoagulants with these and use warfarin with close INR checks.

Monitoring. Creatinine clearance, haemoglobin and weight at least every 6 months, and every 3 months if creatinine clearance is under 60 mL/min or age is 75 or over. The interval in months between renal checks is roughly the creatinine clearance divided by 10.

Adherence. Check at each visit, since missed doses leave the person unprotected, especially with short half-life drugs.

Interactions. NSAIDs, aspirin, SSRIs, strong CYP3A4 and P-gp inhibitors and inducers, amiodarone and macrolides.

Switching to warfarin. Start warfarin and continue the direct oral anticoagulant until the INR is 2.0 or over (check INR before the next dose).

Switching from warfarin. Start the direct oral anticoagulant when INR is under 2.0 (under 3.0 for rivaroxaban).

Stopping. Stop for major bleeding. Reversal: idarucizumab 5 g intravenously for dabigatran, and andexanet alfa or prothrombin complex concentrate 25 to 50 units/kg for factor Xa inhibitors. For warfarin give vitamin K 5 to 10 mg intravenously with prothrombin complex concentrate 25 to 50 units/kg.

Common errors. Under-dosing without meeting the criteria, using a direct oral anticoagulant in mitral stenosis, stopping for minor bleeding, and not re-checking kidney function.

Referral and escalation. Refer for major or recurrent bleeding, stroke on treatment, mechanical valve, pregnancy, or creatinine clearance under 15 mL/min.