Page 60 - Retail Pharmacy March 2021

58 CPD ACTIVITY FROM PAGE 57 of acute VTE and prevention of subsequent VTE, and prevention of stroke in non- valvular AF with a high risk of stroke or systemic embolism.5,8,9 Venous thromboembolism Warfarin is an option for acute VTE, but monotherapy with a NOAC is preferred for most adults. Treatment is needed for at least three months but may be considered long-term depending on the likelihood of recurrence and the person’s bleeding risk.12 Atrial fibrillation Anticoagulation is particularly relevant to older people because of the arrhythmia of atrial fibrillation (AF), which is most commonly seen in older people. AF is the most common arrhythmia seen in clinical practice.2,13 AF is associated with increased risk of stroke, heart failure and death.2 Considering these poor outcomes, particularly in older people, the aim of AF management is to treat and modify risk factors, decide on controlling ventricular rate or maintaining sinus rhythm, and prevent cerebral thromboembolism.13 Classifications of AF are: • Paroxysmal (self-terminating, resolving within seven days). • Persistent (episodes last >7 days, including those terminated by cardioversion). • Long-standing (>1 year). • Permanent.2,13 Regardless of the classification and whether rate or rhythm control is used, all people with AF or flutter need to be considered for an oral anticoagulant to reduce the risk of ischaemic stroke and systemic embolism.2,4 However, treatment needs to be balanced against the risk of bleeding. In Australia, the widely accepted CHA2DS2VA score risk stratification tool is used to determine if the patient is at high or low risk of stroke, and whether an oral anticoagulant is warranted.2 (See Table 1). 1. Includesheartfailurewithreduced ejection fraction, heart failure with preserved ejection fraction. 2. Previous stroke, TIA or systemic embolism. 3. Prior myocardial infarction, peripheral arterial disease or aortic plaque. Note that the CHA2DS2-VA score has superseded the CHA2DA2VASc score, so criteria no longer include a point for female sex. A patient’s risk score is calculated from the sum of criteria. Anticoagulation should be strongly considered if the CHA2DS2- VA score is one or more, unless there are contraindications. Risk of bleeding can be assessed in people with AF by the HAS-BLED bleeding risk scoring system.13 The score will enable modification of risk factors but should not be used to avoid anticoagulation.2 (See Table 2). Anticoagulant use in AF Use of warfarin or a NOAC reduces the relative risk of stroke by about 70 per cent in people with AF.13 Current evidence shows that NOACs and warfarin have similar efficacy in AF when the warfarin dose is adjusted according to laboratory monitoring of the international normalised ratio (INR).2 Despite similar efficacy, NOACs are increasingly preferred because of their lower interaction potential with food or drugs, and they don’t require routine laboratory monitoring.2,13 However, warfarin has an important place in older people with multiple morbidities, concurrent medicines, significant renal or hepatic impairment and those who are well controlled with adherent INR testing.11 Evidence is lacking for the use of NOACs in AF for patients with valvular heart disease, high risk of bleeding, and renal or hepatic impairment. Only warfarin is indicated in valvular AF (moderate to severe mitral stenosis or mechanical heart valve).13 Also, data shows patients whose INR is well controlled may not benefit clinically from switching to a NOAC.2,11 Aspirin and other antiplatelets are no longer recommended as they are less effective than oral anticoagulants, with a similar risk of major bleeding.2,5 Warfarin dosing The dose of warfarin does not change with the indication, unlike the non-vitamin K antagonists/NOACs.4 Warfarin can be started in the community with the use of a recognised local protocol and individualised dosage to achieve a target INR. The usual dosage per the Australian Medicines Handbook (AMH) starts with a 5mg dose once daily for two days, which is then adjusted according to the INR. The usual maintenance dose is 1mg to 10mg once daily, at the same time each day (eg, 4pm to cater for blood sampling the next morning).2,5 Some factors point to a lower maintenance dose. These include older age, severe liver disease, malnourishment, Asian ethnicity, warfarin sensitivity and concurrent medicines that increase warfarin effects.4 Genetic polymorphisms are known to affect the variability of warfarin dosing, but the clinical impact has not yet been established.4 The target INR is two to three for all indications except for prosthetic heart valves, which depends on specialist advice but is usually higher, eg, 2.5–3.5.13 The goal of therapy is to achieve a stable therapeutic INR without over-anticoagulation.2,5 Refer to the Therapeutic Guidelines: Warfarin for an example of an age-adjusted protocol based on baseline INR and subsequent INRs. Warfarin should not be started if the baseline INR is 1.4 or more. In that case, specialist advice is needed.2,4 As response to warfarin takes several days to achieve therapeutic anticoagulation, when immediate anticoagulation is needed (ie, for VTE) a parenteral anticoagulant should also be used until warfarin achieves a therapeutic effect. Immediate anticoagulation is not needed for stroke prevention in patients with AF.4 Warfarin monitoring Regular INR monitoring may be considered an impediment to warfarin use, nevertheless it is a useful tool to assess compliance and treatment response. Some patients find monitoring reassuring and it enables regular contact with a health professional.2 INR should be measured just before starting warfarin, then daily until the INR is stable in the target range. When long-term therapy is stable, INR should be monitored regularly every four weeks or less, as per the AMH.2 If the INR is labile or consistently high, warfarin may not be suitable for ongoing therapy.4 2 2 Criteria Points Stroke risk score Recommended therapy Congestive heart failure1 1 high (2–8) oral anticoagulant Hypertension 1 Age ≥75 years 2 moderate (1) benefit of treatment unclear – decision to use an oral anticoagulant must be individualised Diabetes mellitus 1 Stroke2 2 Vascular disease3 1 Low (0) No antithrombotic required Age 65–74 years 1 Table 1. CHA2DS2-VA score: assessing the need for anticoagulation in non-valvular AF. Source: Table adapted from AMH Aged Care2 RETAIL PHARMACY • MAR 2021