Page 61 - Retail Pharmacy March 2021

CPD ACTIVITY 59 Risk factor Clinical characteristic Points H Hypertension systolic blood pressure >160 mmHg 1 A Abnormal liver OR kidney function dialysis/renal transplantation/serum creatinine 3200 mmol/L cirrhosis or bilirubin 2x upper limit of normal with AST/ALT/ALP 3x upper limit normal 1 each S Stroke 1 B Bleeding history of bleeding or a bleeding diathesis 1 L Labile INRs 1 E Elderly >65 years 1 D Drugs OR alcohol concomitant use of antiplatelets/NSAIDs ≥8 drinks/week 1 each The full effect of a dose change will be reflected in the INR within two to three days.5 If the patient’s condition changes (eg, with cardiac or endocrine disease, infection or gastrointestinal disturbance), or drug therapy changes, or there is a significant change in the diet (eg, green leafy vegetable or alcohol consumption), the INR should be checked more frequently.2 Self-monitoring can be considered for patients on long-term warfarin if the INR is stable and the patient or carer is capable of using a point-of-care device. This should be under the supervision of a clinician to check technique and advise on dose adjustment.4 Pharmacists may play a role in this process. Warfarin safety Warfarin dosing is challenging because of the variability between individuals, narrow therapeutic index, drug and diet interactions, and potential for over-coagulation. Bleeding risk is highest in the first three months of therapy and remains above baseline. Bleeding can occur even when the INR is in the therapeutic range.4 Of course, over-coagulation is a risk factor for major bleeding. If the INR has risen, precipitating factors should be modified if possible.2 If there has been minimal or no bleeding, it could be sufficient to withhold or reduce the warfarin dose with careful subsequent monitoring.4,14 If more rapid treatment is needed, vitamin K1 can be given to reverse the anticoagulant effect of warfarin. The injectable formulation given orally is preferred.2,14 For immediate reversal, prothrombin complex concentrates may be administered in hospital.14 Other risk factors include a recent major bleed or surgery, a low platelet count (thrombocytopenia) and concurrent antiplatelet therapy.4 In addition, caution is needed when the patient has a concurrent disease state with increased risk of bleeding (eg, severe uncontrolled hypertension, severe thrombocytopenia, severe liver disease, alcoholism).2,4 Warfarin should be used cautiously in patients with severe renal impairment or in those with a history of frequent falls. Warfarin use in those with impaired cognition should be supervised.2 Patients taking polypharmacy are at increased risk because of the potential for interactions. See ‘Drug Interactions: warfarin’ in AMH.5 Warfarin in older people Prevalence of risk factors for warfarin- induced intracranial haemorrhage is higher in older people due to more fragile intracranial blood vessels and increased likelihood of concurrent disease, polypharmacy and confusion. Age is Table 2. HAS-BLED score. included in bleeding risk scores such as the HAS-BLED as an important predictor of bleeding.2,15 However, fear of over- anticoagulation causing bleeding has led to underuse in older people.3 A recent US study assessed the influence of age on warfarin dose, time in INR target range, and the risk of major haemorrhage.15 Findings confirmed that older people are more sensitive to the effects of warfarin. Dose requirements for those aged 50–70 years were 10.6 per cent lower than younger patients, while dose requirements in those >70 years were an additional 10.6 per cent lower. The study found middle-aged and ‘elderly’ patients spent more time in the target INR range than younger patients, despite having fewer assessments. It also found the relative risk of haemorrhage increased by 31 per cent for each age category and was significantly higher in the elderly group. That is, despite having more stable INR readings, the risk of bleeding was higher in older people. However, the authors concluded that the benefits of warfarin outweigh the risks, even in older people.15 Role of the pharmacist Pharmacists are well placed to educate patients about warfarin before commencement, including: • Need for regular blood tests and follow-up. • Signs and symptoms of bleeding. • Effect of diet (vitamin K is in some foods, but a normal balanced consistent diet, including green vegetables, should keep vitamin K intake stable.2) • Alcohol intake should not be excessive. • Potential drug interactions. • What to do if a dose is missed. • Risks of stopping treatment without medical advice. • Recommend patients keep a record of their dose and INR results, (See ‘Patient resources’). • Suggest telling other treating health professionals they are taking warfarin. • Be mindful that different warfarin brands have not shown bioequivalence and therefore should not be interchanged.5 • Ask about use of complementary medicines, as they should generally be avoided. There is little information about the safety of combinations, but interactions have been reported with St John’s wort, ginkgo biloba, cranberry products, co-enzyme Q10 and willow bark.2 The Therapeutic Goods Administration has also warned of a theoretical risk of bleeding with fish oil when monitoring patients taking anticoagulants and fish oil together.16 Pharmacists are becoming more involved in INR testing, communication of results, dose adjustment decisions (both with the patient and the doctor) and follow-up. Monitoring would also involve advising patients to tell their pharmacist or doctor of any unexplained bleeding or reddish urine or faeces, or if they develop another illness requiring closer INR monitoring (eg, vomiting).2 If a change in anticoagulant is prescribed, pharmacists should know the process is guided by INR. When switching from warfarin to a NOAC, warfarin should be stopped and the NOAC started when the INR is less than two.13 Conversely, change from a NOAC to warfarin needs specialist advice because of the risk of thrombosis and bleeding, and the contributing factors to INR (NOAC half-life, renal function). During the changeover, close laboratory INR monitoring is needed before the NOAC is stopped.17 TO PAGE 60 RETAIL PHARMACY •MAR 2021