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Known knowns and known unknowns: risks associated with combination antithrombotic therapy
1Clinical Pharmacy Services, Rock Creek Medical Center, Kaiser Permanente Colorado, Denver, CO, USA. samuel.g.johnson@kp.org
Thrombosis Research
|October 3, 2008
Summary
Combining warfarin with antiplatelet therapy significantly increases bleeding risk, outweighing benefits for most patients. Careful consideration of risks versus benefits is crucial when prescribing these medications together.
Area of Science:
- Cardiology
- Pharmacology
- Epidemiology
Background:
- Combination antithrombotic therapy with antiplatelet agents and oral anticoagulants presents a clinical dilemma.
- Evidence-based guidelines for antithrombotic therapy are evolving.
- Assessing bleeding risks in patients on dual therapy is critical.
Purpose of the Study:
- To review current consensus recommendations for antithrombotic therapy.
- To evaluate the risks of bleeding in patients receiving combination antithrombotic therapy.
- To analyze clinical outcomes associated with combination therapy using single-center data.
Main Methods:
- Retrospective, longitudinal pharmacoepidemiologic review of adult patients on warfarin.
- Comparison of anticoagulation-related adverse events and coronary events between monotherapy and combination therapy cohorts.
- Statistical adjustment for confounding factors to assess independent associations.
Main Results:
- Analysis included 2,560 monotherapy and 1,623 combination therapy patients.
- Combination therapy was associated with a higher incidence of anticoagulation-related hemorrhages (4.2% vs. 2.0%).
- Adjusted analysis revealed an independent association between combined warfarin and antiplatelet use and hemorrhagic events (OR=2.75), but not coronary events (OR=0.99).
Conclusions:
- The hemorrhagic risk of combining warfarin with antiplatelet therapy appears to exceed the benefits at a population level.
- Clinicians should carefully weigh the risks and benefits before prescribing antiplatelet therapy to warfarin patients lacking evidence-based indications.
- This study highlights the importance of individualized treatment decisions in antithrombotic therapy.
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