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Switching from Vitamin K Antagonist to Dabigatran in Atrial Fibrillation: Differences According to Dose.

In atrial fibrillation (AF) patients 150mg b.i.d. dabigatran is the standard dose, yet guidelines recommend 110mg b.i.d. when bleeding risk is high. It is unknown to which extend these recommendations are followed in patients switching from vitamin K antagonist (VKA) to dabigatran. The aim of this study was to investigate if AF patients are switched from vitamin K antagonist to the appropriate dose of dabigatran.


METHODS
Using nationwide registries (Aug 22, 2011-Dec 31, 2012) we identified VKA-experienced AF patients with available creatinine values who switched to dabigatran. European guidelines criteria 2012 on dabigatran dosing were examined: age≥80 years, HAS-BLED≥3, estimated glomerular filtration rate (eGFR)<50mL/min/1.73 m2, or use of interacting drugs.


RESULTS
We identified 1,626 VKA-experienced AF patients who switched to dabigatran 110mg (820 patients) or 150mg (806 patients). Patients who switched to 110mg compared with 150mg were older (median age 82 years [Q1-Q3:77-86] vs. 68 years [Q1-Q3:64-74]), more often female (54% vs. 35%), had a higher comorbidity burden, higher proportion with CHA2DS2-VASc score≥2 (98% vs. 80%), and more with a HAS-BLED score ≥ 3 (46% vs. 28%). Patients switched to 110mg had a higher absolute risk of mortality compared to patients switched to 150mg. Overall, 26% were inappropriately dosed and 14% were switched to 110mg although the higher dose was indicated. Further, 39% of patients switched to 150mg fulfilled one or more criteria for 110mg, this mostly driven by high HAS-BLED scores (28.2% of patients on 150mg). Female sex, age>80 years, eGFR<50 mL/min/1.73 m2, drugs interacting with dabigatran, and prior bleeding were associated with switch to 110mg. Patients inappropriately dosed had similar risk of mortality as patients appropriately dosed.


CONCLUSION
Among VKA-experienced AF patients one in four were switched to a dabigatran dose contrary to guideline recommendations.