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Warfarin, DOACS, and COVID-19

OpenSAFELY: impact of national guidance on switching from warfarin to direct oral anticoagulants (DOACs) in early phase of COVID-19 pandemic in England


Background: Early in the COVID-19 pandemic the NHS recommended that appropriate patients anticoagulated with warfarin should be switched to direct acting oral anticoagulants (DOACs), requiring less frequent blood testing. Subsequently, a national safety alert was issued regarding patients being inappropriately co-prescribed two anticoagulants following a medication change, and associated monitoring.

Objective: To describe which people were switched from warfarin to DOACs; identify potentially unsafe co-prescribing of anticoagulants; and assess whether abnormal clotting results have become more frequent during the pandemic.

Methods: Working on behalf of NHS England we conducted a population cohort based study using routine clinical data from >17 million adults in England.

Results: 20,000 of 164,000 warfarin patients (12.2%) switched to DOACs between March and May 2020, most commonly to edoxaban and apixaban. Factors associated with switching included: older age, recent renal function test, higher number of recent INR tests recorded, atrial fibrillation diagnosis and care home residency. There was a sharp rise in co-prescribing of warfarin and DOACs from typically 50-100 per month to 246 in April 2020, 0.06% of all people receiving a DOAC or warfarin. INR testing fell by 14% to 506.8 patients tested per 1000 warfarin patients each month. We observed a very small increase in elevated INRs (n=470) during April compared with January (n=420).

Conclusion: Increased switching of anticoagulants from warfarin to DOACs was observed at the outset of the COVID-19 pandemic in England following national guidance. There was a small but substantial number of people co-prescribed warfarin and DOACs during this period. Despite a national safety alert on the issue, a widespread rise in elevated INR test results was not found. Primary care has responded rapidly to changes in patient care during the COVID-19 pandemic.

Read the full paper on medRxiv here

Plain English Summary

Primary care providers responded rapidly to guidance issued by the NHS during the early phase of the COVID-19 pandemic to switch some patients from warfarin to direct acting oral anticoagulants

Early in the COVID-19 pandemic the NHS recommended that appropriate patients prescribed warfarin (a blood thinning medicine taken to lower the risk of developing a dangerous blood clot) should be prescribed a different type medicine to prevent blood clots, known as a direct acting anticoagulant (DOACs). People taking warfarin have a regular blood test called the international normalised ratio (INR) that measures how long it takes your blood to clot. Depending on the exact result of the INR the dose of warfarin a person takes may go up or down (you can read more about warfarin on the NHS website here). DOAC prevent clots as well but work in a different way to warfarin and people taking DOACs do not require a frequent INR test. They still do require some blood tests, for example measuring how their kidneys work, but these are less frequent and the dose generally remains stable. People taking DOACs generally require less face-to-face blood tests and therefore this would help minimise the risk of spreading the COVID-19 virus.

Researchers from LSHTM and University of Oxford used the OpenSAFELY data analysis platform to securely run analyses across the routinely collected health data of more than 17 million adults in England to investigate:

  1. How many patients were switched from warfarin to DOACs
  2. Whether there was any evidence of unsafe prescribing as a result of the change in guidance
  3. Whether more patients experienced unusual INR results during the first wave of the COVID-19 pandemic

Researchers found that about 12% of patients previously prescribed warfarin were prescribed DOACs instead between March and May 2020. These patients were more likley to be older; have recently had a kidney function test; have had their blood clotting time tested recently; have an irregular heart beat; and to live in a care home. They also found that there was a small rise in the number of people prescribed a DOAC and warfarin at the same time which may be unsafe, although this represented 0.06% of all people receiving a prescription for warfain or a DOAC.

These findings showed that primary care providers responded quickly to the national guidance issued by the NHS and that although there were concerns that more patients might unusual INR results during the first wave of the COVID-19 pandemic, evidence of an increase in unusual INR results was not found.