Warfarin prevalence, indications for use and haemorrhagic events

Area of Science:

• Pharmacology and Therapeutics
• Clinical Audit
• Public Health

Background:

• Warfarin is a standard oral anticoagulant in Ireland, frequently prescribed to elderly patients.
• Audits are crucial for assessing medication safety and patient outcomes in real-world clinical settings.

Purpose of the Study:

• To audit warfarin use in the HSE Mid-Western Area over 12 months.
• To determine the prevalence, indications, and haemorrhagic complications of warfarin therapy.
• To identify factors contributing to over-anticoagulation and assess management strategies.

Main Methods:

• A 12-month audit including all patients on warfarin therapy over a 13-week period (n=2564).
• Analysis of age-standardised warfarin prevalence rates.
• Examination of indications for warfarin, incidence of haemorrhagic events (INR ≥ 5.0), and causes of over-anticoagulation.

Main Results:

• Warfarin prevalence increased with age, reaching 6.1% in 80-84 year olds.
• Atrial fibrillation was the most common indication (54%).
• The annual cumulative incidence of adverse haemorrhagic events with INR ≥ 5.0 was 16.6% (1.3% major, 15.3% minor), with genitourinary and gastrointestinal sites most affected.
• Drug interactions were the most frequent cause of over-anticoagulation (43%).
• Elevated INR was managed by dose adjustment (74%), vitamin K (17%), or blood products (3%).

Conclusions:

• Warfarin therapy is prevalent, especially in the elderly, with atrial fibrillation as a key indication.
• Significant rates of haemorrhagic complications occur with over-anticoagulation, often linked to drug interactions.
• Current management strategies for elevated INR are largely effective, with dose modification and vitamin K being primary interventions.