Appropriateness of Apixaban Dosing to Prevent Stroke in Patients with Atrial Fibrillation: A Pilot Study.

BACKGROUND: The ARISTOTLE study investigated apixaban, at a dose of 5 mg PO bid, for the prevention of stroke in patients with atrial fibrillation; however, it has been noted anecdotally that many patients are receiving 2.5 mg PO bid, despite being eligible for the full dosage. A recent study examining the use of dabigatran and rivaroxaban found that many patients were receiving these medications inappropriately; however, a literature search conducted in April 2016 showed that apixaban had not been formally studied in this context. OBJECTIVE: To evaluate the appropriateness of apixaban dosing for stroke prevention in patients with atrial fibrillation, relative to the dose used in the ARISTOTLE study and recommendations in the product monograph. METHODS: This retrospective chart review was conducted at a 300-bed Canadian teaching hospital. All inpatients with atrial fibrillation for whom apixaban was prescribed for stroke prevention in March 2015 were considered for inclusion. The appropriateness of apixaban dosing was determined in relation to the ARISTOTLE methodology and product monograph recommendations (i.e., 5 mg PO bid, with a lower dosage of 2.5 mg PO bid if warranted on the basis of age, weight, or serum creatinine level). RESULTS: A total of 47 patients were included, of whom 25 (53%) were receiving apixaban inconsistent with the ARISTOTLE study and the product monograph. Limitations of the current study included small sample size, single-centre setting, and retrospective design, which precluded determination of each prescriber's rationale for dosage choice. CONCLUSIONS: Pharmacists and physicians should be vigilant in ensuring that patients with atrial fibrillation are receiving the appropriate dosage of apixaban to optimize the risk-benefit ratio of this therapy.