Prevalence and predictors of inappropriate dosing of direct oral anticoagulants

Background Information on inappropriate dosing of direct oral anticoagulants (DOACs) is scarce in the Australian context. Aim To describe the prevalence and potential predictors of inappropriate dosing of DOACs. Methods Patients who received DOACs during admission under a general medical unit over a 2‐year period (from January 2017 to December 2018) were retrospectively studied. Appropriateness of the dosing regimen was verified against the recommendations of the Therapeutic Goods Administration of Australia. Data were obtained from medical records and analysed in univariate and multivariate logistic regression models. The variables associated with under‐ and overdosing were also determined. Results A total of 203 (mean age 71.6 ± 14.5 years, females 52%) patients were studied. Inappropriate dosing occurred in 44 (22%) patients: underdosing 27 (13%) and overdosing 17 (8%). Age ≥75 years ( P < 0.01), lower estimated creatinine clearance (CrCl) ( P < 0.01), prescription of DOAC prior to index admission ( P < 0.01) and higher Charlson Comorbidity Index ( P < 0.01), HAS‐BLED ( P < 0.01) and CHA 2 DS 2 ‐VASc ( P < 0.01) scores had a significant univariate association with inappropriate dosing. However, in the multivariate logistic regression only lower CrCl (odds ratio (OR) 1.04, 95% confidence interval (CI): 1.01–1.07, P < 0.01) and prescription of DOAC prior to index admission (OR 2.62, 95% CI: 1.01–6.75, P = 0.047) remained significantly associated with inappropriate dosing. Impaired renal function also had a significant association with underdosing (OR 1.04, 95% CI: 1.01–1.07, P = 0.01) and borderline significance with overdosing (OR 1.03, 95% CI: 1.00–1.07, P = 0.06). Conclusion Inappropriate dosing of DOACs, especially underdosing, is common in clinical practice. Clinicians should exercise due diligence when prescribing DOACs to patients with renal impairment and in outpatient settings.