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CDHB

Prevention of Stroke and Systemic Embolism in Atrial Fibrillation (AF)

• The prevention of arterial embolism in chronic AF has until recently relied upon aspirin or warfarin.
• Dabigatran, a direct inhibitor of thrombin, has been funded (July 2011) to prevent embolism in AF.
• The choice between warfarin and dabigatran will need careful consideration.
• Warfarin has many advantages; it is inexpensive, has no known late effects, the anticoagulation effect can be reversed, and many patients are easily stabilized on the drug.
• Dabigatran and similar drugs may be useful for patients who dislike venepuncture, are difficult to stabilize on warfarin, live away from blood testing centres, or travel frequently. Dabigatran has fewer known drug interactions than warfarin, but caution is needed with the concurrent use of P-gp inhibitors such as verapamil, amiodarone and ketoconazole, and with P-gp inducers, e.g., rifampicin. Dabigatran is not affected by diet. Its half-life is short (approximately one third that of warfarin in the setting of normal renal and hepatic function) but its anticoagulant effect cannot be reversed. Currently dabigatran is considerably more expensive than warfarin.
• There is an increased risk of bleeding if either warfarin or dabigatran are given with antiplatelet drugs.

Management

• Warfarin should be given with the usual precautions. See Treatment of VTE.
• Dabigatran is registered and funded for clot prevention in AF. This drug is excreted mainly by the kidney, so dosing appropriate to renal function is important. Dabigatran has a fraction excreted unchanged in the urine (fu) of 0.8.
  • Dabigatran when used to prevent thrombosis in atrial fibrillation: the standard recommended dose is 150 mg BD PO. This drug should be used with caution in the elderly, and a lower dose of 110 mg BD PO is recommended for patients over 80 years old.
  • Dosage in renal impairment:
    • The first dose is the same as the standard recommended dose for the indication.
    • Subsequent doses are adjusted if the creatinine clearance (CrCl) is <80 mL/minute (Cockcroft and Gault), as shown in the table below, based on the fu of 0.8.
    • Doses may need to be rounded to accommodate the available capsule sizes (75 mg, 110 mg, 150 mg).

• Before using dabigatran, refer to:
  • The PHARMAC website Guidelines for testing and perioperative management of dabigatran and Guidelines for management of bleeding with dabigatran.
  • The Medsafe datasheet on dabigatran.
  • The CDHB Clinical Pharmacology bulletin on dabigatran etexilate (July 2011).

Topic Code: 36440