30 Appropriate DOAC dosing: an evaluation for real world cardiology

Abstract

Introduction Atrial fibrillation (AF) affects 2.4% of the English population. Direct oral anticoagulants (DOACs) are often used to reduce stroke risk. DOACs require dose adjustments according to creatinine clearance (CrCl). We evaluated DOAC prescribing in AF in an acute UK cardiology ward and evaluated whether eGFR can be used as an alternative to CrCl. Methods We examined all DOAC discharge prescriptions on the cardiology ward at NSECH, Cramlington from Nov 2015-Nov 2016. We retrospectively recorded DOAC dose, serum creatinine and eGFR pre-discharge. Weight was obtained from hospital paper records for those patients with eGFR reflecting a degree of renal impairment. We reviewed notes for patients prescribed apixaban or dabigatran at full dose with eGFR 35 and those prescribed rivaroxaban or edoxaban at full dose with eGFR 45. For those, CrCl was calculated using the Cockcroft-Gault equation. Summary product characteristics (SPC) dosing guidelines were used to define appropriate dosing. Results We identified 225 DOAC prescriptions for AF in 168 patients. Whilst the majority of DOAC prescriptions were appropriate, this study identified 11% (25) of discharge DOAC prescriptions for AF did not follow SPC guidelines (figure 1). Full dose DOAC was prescribed inappropriately in 3% (8). The other 8% (16) had inappropriate dose reduction. 55 discharges were identified as reflecting a degree of renal impairment. Comparison of CrCl and eGFR in those 55 discharges found 22% (12) would have over-estimated renal function had eGFR been used to make drug dosing decisions, leading to incorrect prescriptions of the full dose. Similarly renal function would have been under-estimated by eGFR in 13% (7 out of 55) of cases using eGFR alone which would have led to inappropriate reduced dose DOAC. Conclusion and implications This study reminds clinicians to remain vigilant about DOAC dose modifications. We demonstrated the importance of the CrCl for patients with impaired renal function as the eGFR provides an inaccurate estimate that may lead to inappropriate DOAC dosing. Inappropriate dose reduction appeared more common than inappropriate full dose. This is in keeping with published literature form a US cohort.1 Failure to reduce DOAC doses may increase bleeding without additional efficacy. Inappropriate dose reductions are often carried out to mitigate bleeding risks but is associated with overall worse outcomes.1 Our findings were from a unit with 7 day cardiologist input and dosing errors may be even more frequent in the non-specialist environment. We addressed this by designing educational material for the hospital teams (figure 2). Reference . Yao X, Shah ND, Sangaralingham LR, et al. Non-vitamin k antagonist oral anticoagulant dosing in patients with atrial fibrillation and renal dysfunction. J Am Coll Cardiol2017;69:2779–2790.