Over‐Anticoagulation in Elderly Warfarinised Patients

Aim To identify factors that contribute to over‐anticoagulation in elderly warfarinised patients and to review the management of over‐anticoagulation. Method A prospective cohort audit was conducted over 6 months (1 February to 31 July 2011) at a teaching hospital. Inpatients with an international normalised ratio (INR) > 4 were identified via a daily automated pathology screening report. Medical notes and drug charts of eligible patients were reviewed and data (medical history, drug history, warfarin regimen, INR results, clinical events, management of over‐anticoagulation) were compiled. Results 62 patients prescribed warfarin were identified as experiencing over‐anticoagulation. 32 (52%) patients had INRs > 4 and 12/32 (38%) patients had documented bleeding of clinical significance. Most patients had 2, 3 or 4 risk factors for over‐anticoagulation. Prevalent risk factors were: age > 65 years (92%), co‐prescribing warfarin with interacting medications (76%) and renal insufficiency (21%). Co‐prescribed medications that interact or potentiate the effects of warfarin included antibiotics (47%) and non‐steroidal anti‐inflammatory drugs (21%). Most patients with INRs > 4 were managed by withholding warfarin and administering a small dose of vitamin K. Conclusion Warfarin over‐anticoagulation was prevalent among elderly patients and those prescribed interacting medications. A conservative approach to the management of over‐anticoagulation was appropriate for most cases.