The effect of drug interactions on bleeding risk associated with warfarin therapy in hospitalized patients

Abstract

Background. Bleeding is a serious adverse drug reaction associated with warfarin therapy, often induced by interacting co-medication.

Methods. We investigated the frequency and clinical consequences of warfarin drug interactions utilizing medical records of 6,772 warfarin-treated in-patients of Turku University Hospital.

Results. A total of 48% of warfarin-treated in-patients were exposed to interacting co-medication. Adjusted odds ratio (OR) for bleeding was highest for cytochrome P450 2C9 (CYP2C9) inhibitors (OR 3.6; 95% confidence interval (CI) 2.4–5.6). Non-selective non-steroidal anti-inflammatory drugs (NSAID) and coxibs were associated with a bleeding risk of a similar magnitude (OR 2.6; 95% CI 1.6–4.2 and OR 3.1; 95% CI 1.4–6.7, respectively). Selective serotonin re-uptake inhibitors (SSRI) were associated with a remarkably higher bleeding risk than non-SSRIs (OR 2.6; 95% CI 1.5–4.3 and OR 1.2; 95% CI 0.3–4.3, respectively). Odds ratio for bleeding in the platelet aggregation inhibitor group was 1.6 (95% CI 0.8–3.1).

Conclusion. We conclude that co-medication in warfarin-treated in-patients is common and should be carefully evaluated to decrease the bleeding risk associated with warfarin therapy.

• Antidepressants
• coxibs
• CYP2C9 inhibitors
• drug interactions
• hemorrhage
• NSAIDs
• platelet aggregation inhibitors
• warfarin