Antibiotic treatment and major bleeding amongst oral anticoagulant users

End of project summary

Main messages

The main oral anticoagulants (“blood thinning medication”) used in the UK are warfarin and a group of drugs known as Direct Oral Anticoagulants, or DOACs. Their main use is to prevent blood clots and stroke in people with an irregular heart rhythm. Bleeding is the most serious complication of using anticoagulant medication. It is well recognised that people with serious infections, such as sepsis, can experience problems with their blood coagulation pathways with subsequent bleeding. However, it is unclear whether similar issues may arise with less serious, more common infections, that are treated in the community, particularly amongst people who use oral anticoagulants and are thus more susceptible to bleeding. 

In this research, we aimed to determine the risk of bleeding amongst oral anticoagulant users who presented to General Practice with symptoms of a community acquired respiratory tract infection (RTI). 

Our main findings were: 

• People who use oral anticoagulants are more than twice as likely to experience a bleed in the 2-week period following consultation for an RTI, than during times without an RTI. 
   
• The types of bleeds experienced included major bleeds like brain and stomach haemorrhage that required hospital admission, and non-major bleeds such as nose bleeds, blood when coughing, and blood in the urine. 
   
• When we compared people with an RTI who were prescribed immediate antibiotics to those who were not prescribed antibiotics, we found that those prescribed immediate antibiotics had a 40% lower risk of major bleeding and a 22% lower risk of non-major bleeding, compared to those not. 
   
• Our work has implications for how patients and clinicians manage oral anticoagulant use during an acute infection and warrants further investigation to fully understand the potential risks and how they might be mitigated. A key issue is to understand why and how antibiotics may reduce the risk of bleeding and whether a lower threshold for antibiotic use for RTIs in this population may be beneficial. However, this needs to be weighed up against the broader individual and societal harms associated with overuse of antibiotics and development of antibiotic resistance.