Misdosing of Non-Vitamin K Antagonist Oral Anticoagulants in Primary Care.

Purpose: Prescription patterns of non-vitamin K antagonist oral anticoagulants (NOACs) are unknown among primary care physicians, where most patients with nonvalvular atrial fibrillation (NVAF) are diagnosed and followed up. The goal of this study was to evaluate overdosing and underdosing of NOACs in patients with NVAF followed up in primary care and determine their clinical predictors.

Methods: This multicenter cross-sectional study included all patients with NVAF followed up in 13 primary care units in the center region of Portugal. Patients receiving antithrombotic regimens other than NOACs and patients with missing data were excluded.

Findings: The study included 858 patients with NVAF on an NOAC regimen. Overall, 30.3% were prescribed an off-label dosage (25.4% with infratherapeutic dosing [ITD] and 4.9% with supratherapeutic dosing). Chronic kidney disease (odds ratio, 14.0; 95% CI, 5.4-36.5; P < 0.001) and female sex (odds ratio, 2.6; 95% CI, 1.2-5.7; P < 0.001) were independent predictors of supratherapeutic dosing. We also found a significant effect of chronic kidney disease on ITD (odds ratio, 0.22; 95% CI, 0.258-0.678; P < 0.001).

Implications: In primary care, NOACs are frequently prescribed with unadjusted dosages, generally infratherapeutic. Attention should be paid to women and patients with chronic kidney disease.