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

Curtis, H. J.; MacKenna, B.; Walker, A. J.; Croker, R.; Mehrkar, A.; Morton, C. E.; Bacon, S.; Hickman, G.; Inglesby, P.; Bates, C.; Evans, D.; Ward, T.; Cockburn, J.; Davy, S.; Bhaskaran, K.; Schultze, A.; Rentsch, C. T.; Williamson, E.; Hulme, W.; McDonald, H. I.; Tomlinson, L.; Mathur, R.; Drysdale, H.; Eggo, R. M.; Wing, K.; Wong, A.; Forbes, H.; Parry, J.; Hester, F.; Harper, S.; Evans, S. J.; Douglas, I. J.; Smeeth, L.; Goldacre, B.

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). Conclusions 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.