Frequent need for apixaban dose adjustment for atrial fibrillation in an unselected acute medical admission population during the COVID 19 pandemic

Abstract

Abstract Funding Acknowledgements Type of funding sources: None. Background During the COVID-19 pandemic, systematic switching patients of eligible patients with atrial fibrillation from warfarin to direct oral anticoagulants (DOACs) was encouraged to simplify drug dosing and obviate the need for regular monitoring. Regional exclusions to switching included mechanical heart valves, moderate to severe mitral stenosis and stage 5 chronic kidney disease (estimated glomerular filtration rate [eGFR]< 15ml/min/1.73m2). However, each DOAC requires dose adjustment depending on renal function and other patient factors. Purpose Failure to dose reduce when indicated leads to excessive serum drug concentration and increased risk of major haemorrhage, particularly in patients who are acutely unwell. We thus quantified the likelihood of need for dose adjustment in an unselected acute medical admission population. Methods While on call, a single investigator prospectively identified all patients admitted on the acute medical or cardiology take-in between 1/12/21 and 1/2/22 who were taking apixaban for atrial fibrillation. Apixaban was selected as the study DOAC as it was the most commonly used DOAC but had the most complex dose adjustment algorithm and hence risk of dose error. In order to determine the appropriate drug dosage, patient age, weight, serum creatinine and eGFR were recorded. Dose reduction to 2.5mg was required if the patient meet 2 of the following 3 criteria of [age>80 years, weight <60kg, serum creatinine >133umol/l], or a single criterion, had an eGFR <30ml/min/1.73m2. Drug discontinuation was required if eGFR was <15ml/min/1.73m2. Results All patients identified (n=50) had a CHA2DS2-VASc score of ≥2. Patients with active COVID-19 infection were excluded. Mean age was 77.2 years (range 46-102). Mean weight was 78kg (range 52-101). Mean serum creatinine was 212umol/l (range 62-595). Mean eGFR was 33ml/min/1.73m2 (range 8 to >60). Of the 50 patients, 24 (48%) were taking the appropriate apixaban dose on admission which did not require dose adjustment (18 of whom were appropriately taking 5mg bd and 6 were taking 2.5mg bd). Dose reduction from 5mg bd to 2.5mg bd was required in 17 (34%) patients. Stopping treatment, at least temporarily due to eGFR<15ml/min/1.73m2, was indicated in 9 (18%) of patients. No patient required an increase in drug dose. (Graph 1) Conclusion Over half of acute medical or cardiology patients admitted within a COVID-19 setting and taking apixaban for atrial fibrillation required at least temporary drug dose adjustment or discontinuation. Clinicians should expect that adjustment of apixaban dose may be required during acute admission.