MedWire News: Clopidogrel antiplatelet therapy significantly increases the risk for bleeding in patients using vitamin K antagonist therapy, demonstrates research from Utrecht University in The Netherlands.

While aspirin has been show to increase bleeding risk in patients using coumarin therapy, the effect of the newer antiplatelet drugs clopidogrel and dipyridamole is yet unknown, explain Tom Schalekamp and co-workers.

To investigate, the team examined linked data from Dutch pharmacy and hospital records and identified 1848 patients who were diagnosed with major bleeding while taking coumarin. These patients were each matched with four coumarin users without a history of bleeding.

As reported in the journal Thrombosis and Haemostasis, patients who used aspirin or clopidogrel were significantly more likely to experience major bleeding than those who used neither agent (odds ratio [OR]=2.9 and 1.6, respectively).

A strong trend toward increased bleeding risk was also identified for patients who used dipyridamole or a combination of antiplatelet agents, but this did not reach statistical significance (OR=1.5 and 1.8, respectively).

The risk for bleeding was mostly attributed to gastrointestinal bleeding, with ORs for this outcome for aspirin, clopidogrel, dipyridamole, and combination antiplatelet agent therapy at 2.1, 3.6, 2.2, and 2.4, respectively.

“The results of our study give rise to some clinical considerations,” Schalekamp et al write in the journal Thrombosis and Haemostasis.

Noting that the American College of Chest Physicians recommends warfarin users unable to use aspirin take dipyridamole or clopidogrel, the team concludes: “Our findings do not support the view that adding clopidogrel or dipyridamole to coumarins is safer than adding low-dose aspirin to coumarins."

Free abstract