Skip to main content

Project #46:
OpenSAFELY: impact of national guidance on switching anticoagulant therapy during COVID-19 pandemic


From the beginning of the COVID-19 pandemic, the NHS recommended putting measures in place to reduce face-to-face contact with patients where possible to reduce the risk of transmission. This included guidance to consider switching warfarin patients to a direct acting oral anticoagulant (DOAC) where suitable. This aimed to reduce the number of times patients had to attend for blood tests. However, it was not known how widespread this practice was, whether it resulted in potentially dangerous co-administration of both drugs in some patients, or whether those patients who remained on warfarin were tested frequently and maintained good clotting results.

We identified patients who were taking warfarin prior to the pandemic and the factors associated with being switched to DOACs.

This is the first widespread study on the impact of the NHS England guidance. We showed that a substantial number of patients in general practice in England had their anticoagulant switched from warfarin to a DOAC. We also showed that there was a small number of patients who potentially received both warfarin and a DOAC. There did not appear to be a widespread reduction in INR control during the pandemic.

This study highlights that national prescribing guidance can be implemented in primary care in England, both on a large scale and at a fast pace when necessary to improve patient care. It also highlights the importance of good clinical governance processes when switching medications, in order to reduce the risk of co-prescribing of both agents.


  • Study leads: Helen Curtis
  • Organisation: University of Oxford and London School of Hygiene and Tropical Medicine