This page gives advice on management of patients taking warfarin in primary care during the Covid-19 pandemic
Advice on drug monitoring for other medicines during Covid-19 is here
Normal practice is to monitor INR up to a maximum of every 12 weeks
During the Covid-19 pandemic, recommendations to help minimise attendances include the following
1) For patients with prior DVT or PE and where risk of recurrence is now low, consider stopping warfarin
2) For other patients, consider switching to a DOAC; however, DO NOT switch if the patient:
- has prosthetic mechanical valve; consult cardiologist
- has moderate to severe mitral stenosis
- has antiphospholipid antibody syndrome (APLS)
- is pregnant, breastfeeding or planning pregnancy
- requires a higher INR than the standard INR range of 2.0–3.0
- has severe renal impairment (creatinine clearance < 15ml/min)
- takes interacting medicines such as certain HIV antiretrovirals or hepatitis antivirals (check HIV drug interactions)
3) If the patient is in a category below, seek specialist anti-coagulation advice prior to switching to a DOAC:
- has active malignancy and/or chemotherapy
- takes phenytoin, carbamazepine, phenobarbitone or rifampicin
- has venous thrombosis at unusual sites
- is on triple therapy i.e. dual antiplatelet plus warfarin
4) Where switching to a DOAC is possible, follow Royal Pharmaceutical Society advice; in addition:
- If a switch to a DOAC is being considered across a patient cohort, take a phased approach over the 12 week cycle to protect the supply chain for all patients
- Consider prioritising patients (i.e. switching first) with poor control of their INR as this cohort will require the most frequent INR checks.
5) Where warfarin remains necessary, a number of options exist to help minimise attendances for INR monitoring
- Advice on extending INR testing intervals
As many stable patients as possible should continue to have their INR monitored at no less frequently than every 12 weeks, as this is the international guidance. Self-monitoring and community INR monitoring are options to reduce attendances; however:
- Where patients normally have their INR monitored more frequently than 12 weekly, consider moving to 12 weekly where safe to do so
- Patients should be reminded to contact their INR monitoring service via telephone if they experience COVID-19 symptoms.
- If patients show symptoms of COVID-19 it is not appropriate to extend the INR monitoring interval. Monitor patients INR within 1-7 days, the exact timing of the INR should take into account relevant factors including: whether patient has symptoms of bleeding, is taking antibiotics or other new interacting medicine(s), is feeling unwell, has reduced food intake, has recent alcohol consumption. See options below
- Self monitoring
Increasing self-monitoring may help reduce both attendances and INR monitoring workload across the system.
- Patients or family members need to be carefully selected for use of CoaguChek, taking into account their manual dexterity, cognitive function, vision and ability to use the technology.
- Patients or family members living with them will need to be taught to self-test their INR using a CoaguChek machine (providing this can be obtained) and to phone in the results.
- There are challenges associated with implementation: e.g. purchasing equipment, providing test strips, training patients, and undertaking quality assurance checks.
Further advice on self-monitoring can be found from NICE in their diagnostic guidance DG14.
- Community monitoring via teams visiting patients
Continuation of the safe monitoring of INR for patients in the community when isolated for long periods during COVID-19 is essential.
Home visiting phlebotomy services linked to INR monitoring services (e.g. GP surgeries or Community trusts) will be key to continued safe monitoring of patients on warfarin during COVID-19.
Services monitoring patients with suspected COVID-19 should give particular consideration to the timing of the blood test (i.e. to be arranged at the end of a phlebotomy/nursing shift) and they should follow local guidance for blood tests for suspected/confirmed COVID-19 positive patients.
- Other options
For other patients in whom DOACs are not an option, consider a Low Molecular Weight Heparin (LMWH) if the patient can be taught to self-inject or a family member living with them can administer the injection.
As a last resort, for individual patients where INR testing cannot be carried out and therefore warfarin cannot be dosed safely, warfarin therapy could be temporarily stopped. Any decision to stop must take into account the balance of benefit and risk for the individual patient, and should include discussion with both the patient and advice sought from the anticoagulation clinic. Regular review should be undertaken with a view to restarting warfarin as soon as is safely possible.
Note that patients with mechanical valves in situ must continue on warfarin at all times, and cardiologist advice should be sought where regular INR testing cannot be undertaken.
This page was developed in conjunction with Helen Williams, Consultant Pharmacist for Cardiovascular Disease and Clinical Director for Atrial Fibrillation, Southwark CCG and Health Innovation Network, South London and Dr Frances Akor, Consultant Pharmacist, Anticoagulation, Imperial College Healthcare NHS Trust.
This advice has been developed quickly in response to the COVID-19 pandemic; if you spot anything that’s wrong report a concern to us.