Prophylaxis of Stroke and Systemic Embolism in Non-valvular Atrial Fibrilliation (AF)
Anticoagulation General Notes
- Refer to NICE NG196 and ESC guidelines on atrial fibrillation.
- Clinical Knowledge Summaries provide a comprehensive overview in relation to oral anticoagulation and includes information that patients should be given prior to treatment and monitoring that should be carried out. Information on switching between anticoagulant regimens is also included.
- Anticoagulation should not be withheld solely because of a person’s age or their risk of falls.
- Indication and duration of treatment should be clearly recorded at initiation of treatment; the patient-held anticoagulant treatment booklet should be used. See BNF for details.
- Patients should be warned of the hazards of treatment with anticoagulants. In particular, they should be aware of the need to report symptoms such as bruising. Patients should be provided with safety netting advice on signs of clinically relevant bleeding or clotting (e.g. FAST mnemonic) and when it is important to represent to hospital.
- Anticoagulant alert cards must be carried by patients and can be ordered by e-mailing the HSC Business Services Organisation at the following address pharmacystationeryorders@hscni.net.
- The anticoagulant effect of DOACs fades rapidly 12 to 24 hours after the last intake. Therefore strict compliance by the patient is crucial for adequate protection. Refer to individual SPC for ‘missed dose’ guidance for each DOAC. In contrast, the anticoagulant effect of warfarin persists for several days after the last warfarin dose.
Prescribing Notes
DOAC prescribing notes
- Apixaban is recommended as first choice DOAC for AF.
- Rivaroxaban is the most cost-effective once-daily choice where compliance is an issue.
- Rivaroxaban must be taken with food. The MHRA has received a small number of reports suggesting a lack of efficacy (thromboembolic events) in people taking 15 mg or 20 mg rivaroxaban tablets on an empty stomach.
- Dabigatran capsules cannot be crushed or opened and cannot be used in standard compliance aids due to the instability of the drug. Some packs have short expiry dates once opened, therefore prescribers should, where possible, prescribe in full packs.
- Patients at extremes of body weight (i.e. <50kg or >120kg) were under-represented in initial DOAC clinic trials. For patients weighing more than 120kg, there has historically been a degree of caution surrounding the use of DOACs due to concerns of sub-therapeutic effect. Evidence is now available to support the use of apixaban and rivaroxaban at standard doses in patients weighing 120kg to 150kg as recommended by the International Society of Thrombosis and Haemostasis (ISTH). Assays for DOAC therapeutic monitoring are of limited clinical use and not required. Warfarin is generally preferable >150kg (BMI approximately 50kg/m2).
- Calculating creatinine clearance (CrCl) for DOACs:
- CrCl calculators embedded within GP IT systems do not give a reliable estimate of CrCl for the adjustment of DOAC doses and are not recommended
- The use of a web based application such as MDCalc is suggested where actual bodyweight is used to calculate the CG CrCl. If in addition the patient’s height is added the different weight method calculations (modified for body weight) can be seen giving a range of possible values for CrCl.
- Edoxaban should be used in patients with NVAF and high CrCl only after a careful evaluation of the individual thromboembolic and bleeding risk (potential for reduced efficacy).
- Renal function should be monitored at initiation and at least annually for patients taking DOACs. Ensure any necessary dose reductions are made.
Warfarin prescribing notes
- Warfarin is recommended where DOACs are contraindicated, not tolerated or not suitable in patients with AF. This includes:
- patients with mechanical prosthetic valves or significant mitral stenosis
- patients with severe renal dysfunction (CrCl<15mL/min)
- Only warfarin 1mg and 3mg tablets should be prescribed.
- Vitamin K (phytomenadione) can be given to reverse the effects of warfarin but takes 6 to 12 hours to become effective. If rapid reversal of warfarin is required, specialist haematological advice on the agreed regional policy should be sought. See also BNF.
Cautions
- A lower initial loading dose of warfarin is recommended in patients aged over 70 years.
- There are many clinically important interactions with warfarin -consult BNF before prescribing.
- The MHRA reminds healthcare professionals of the bleeding risk with DOACs and of the importance that patients receive an appropriate dose based on renal function.
- DOACs are contraindicated in the setting of mechanical (metallic) valves. They may be used in bioprosthetic valves after 3 months post operatively. This is in line with EHRA guidance (see Table 1); recommendations in SPC may differ.
- DOACs are contraindicated in the setting moderate to severe mitral stenosis but may be used with other native valvular disease (see EHRA guidance, Table 1).
- Guidance on the management of dental patients taking anticoagulants or antiplatelet drugs by the Scottish Dental Clinical Effectiveness Programme (SDECP) has been adopted for use in Northern Ireland and is available at sdcep.org.uk.
- Specialist haematological advice should be sought regarding strategies for the reversal of the anticoagulant effects of DOACs.
- Specific reversal agents for dabigatran (idarucizumab) and the factor Xa inhibitors apixaban and rivaroxaban (andexanet alfa▼) are now available. These are for hospital only use.
- Refer to BNF for full details of cautions, contraindications and interactions with DOACs.