Pharmacodynamic Effects of Dabigatran in Patients on Dual Antiplatelet Therapy

Dual antiplatelet therapy consisting of aspirin and clopidogrel is the cornerstone of
treatment for prevention of atherothrombotic events in patients with coronary artery disease
(CAD) undergoing percutaneous coronary interventions (PCI). Many patients on dual
antiplatelet therapy in this setting may be affected by other thromboembolic conditions, in
particular atrial fibrillation, therefore having an indication to also receive oral
anticoagulation for stroke prevention. Thus, a considerable percentage of patients are under
"triple therapy" which consists of aspirin plus clopidogrel plus an oral anticoagulant.
Although this combination therapy allows a reduction of atherothrombotic and thromboembolic
events, patients on triple therapy are at an increased risk of bleeding complications.

Dabigatran, a synthetic, reversible direct thrombin inhibitor, has been studied as an
alternative to warfarin in patients with atrial fibrillation and has been shown to be at
least as efficacious with a favorable safety profile. In particular, dabigatran at a dose of
110 mg is associated with rates of stroke and systemic embolism similar to warfarin, with
lower rates of major hemorrhage, while a dose of 150 mg is associated with lower thrombotic
events with similar rates of bleeding events. These findings have led the Food and Drug
Administration (FDA) to approve dabigatran for use in atrial fibrillation patients in
December 2011 and this has also been implemented in practice guidelines to be a superior
strategy to warfarin. However, the FDA only approved the 150mg formulation.

Dabigatran has high affinity and specificity for its target serine protease thrombin, and
one small study shows that dabigatran produced potent inhibition of thrombin-induced
platelet aggregation in vitro. However, there are no studies assessing the ex vivo
pharmacodynamic effects of dabigatran in patients on dual antiplatelet therapy. The ever
raising population with CAD warranting triple therapy and the growing number of patients
being treated with dabigatran underscores the importance of understanding the
pharmacodynamic effects of this treatment regimen.

Inclusion Criteria:

- Patients with known CAD

- On maintenance treatment with aspirin (81 to 325mg per day) and clopidogrel (75 mg
per day) for at least for at least 4-weeks as per standard of care.

- Age between 18 and 80 years old.

Exclusion Criteria:

- Transient ischemic attack or ischemic stroke in the past 6 months.

- Prior hemorrhagic stroke (irrespective of timing).

- Known allergies to dabigatran.

- On treatment with Coumadin derivate or have an indication to be on Coumadin
treatment (atrial fibrillation, prosthetic valve, DVT/pulmonary embolism).

- Platelet count <80x106/mL

- Active bleeding or hemodynamic instability.

- Creatinine clearance <30 mL/minute.

- Baseline ALT >2.5 times the upper limit of normal.

- Hemoglobin < 10 gm/dL

- Pregnant females*. *Women of childbearing age must use reliable birth control (i.e.
oral contraceptives) while participating in the study.