Bleeding Following Warfarin and Amoxicillin/Clavulanate Drug Interaction: A Case Report

Anticoagulants are drugs that prevent blood clotting; however, inappropriate use can also increase the risk of blood clots or bleeding. Warfarin is a commonly prescribed anticoagulant, but its narrow therapeutic index and potential for drug interactions can make it challenging to manage. Direct oral anticoagulants have reduced the use of warfarin; however, it remains the preferred option for some patients. Clinicians must also be aware of drug-drug interactions, such as those between warfarin and antibacterial agents, such as amoxicillin-clavulanic acid (AMC). A case study is presented where an interaction between warfarin and AMC resulted in an elevated international normalized ratio (INR) and bleeding.

Case Report: 

A 64-year-old man with a history of hypertension, ischemic heart disease, and atrial fibrillation presented to the emergency department with new onset epistaxis. He was taking aspirin, metoprolol succinate, and warfarin, which had been in the therapeutic range for over a year. Two weeks before, he had been prescribed AMC for acute sinusitis without any dosage adjustments to his warfarin. Laboratory tests revealed an elevated INR of 5.6 and microscopic hematuria. The patient was treated with nasal packing and vitamin K, and his INR returned to normal. The case highlights the importance of monitoring drug interactions when prescribing anticoagulants.

Drug interactions between warfarin and AMC can cause bleeding complications and require close monitoring. Healthcare providers should consider alternative antibiotics for patients taking warfarin.