Relationship between plasma dabigatran concentration and activated partial thromboplastin time in Japanese patients with non‐valvular atrial fibrillation

<jats:title>Abstract</jats:title><jats:sec><jats:title>Background</jats:title><jats:p>Activated partial thromboplastin time (aPTT) is recommended for monitoring anticoagulant activity in dabigatran‐treated patients; however, there are limited data in Japanese patients. To clarify the relationship between plasma dabigatran concentration and aPTT, we analyzed plasma dabigatran concentration and aPTT at various time points following administration of oral dabigatran in a Japanese hospital.</jats:p></jats:sec><jats:sec><jats:title>Methods</jats:title><jats:p>We enrolled 149 patients (316 blood samples) with non‐valvular atrial fibrillation (NVAF) who were taking dabigatran. Patients had a mean age of 66.6±10.0 years (range: 35–84) and 66% were men. Plasma dabigatran concentrations and aPTT were measured using the Hemoclot<jats:sup>®</jats:sup> direct thrombin inhibitor assay and Thrombocheck aPTT‐SLA<jats:sup>®</jats:sup>, respectively. Samples were classified into eight groups according to elapsed times in hours since oral administration of dabigatran.</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>Significantly higher dabigatran concentrations were observed in samples obtained from patients with low creatinine clearance (CLCr) (CLCr<50 mL/min). Dabigatran concentrations and aPTT were highest in the 4‐h post‐administration range. Additionally, there was a significant correlation between plasma dabigatran concentrations and aPTT (<jats:italic>y</jats:italic>=0.063<jats:italic>x</jats:italic>+32.596, <jats:italic>r</jats:italic><jats:sup>2</jats:sup>=0.648, <jats:italic>p</jats:italic><0.001). However, when plasma dabigatran concentrations were 200 ng/mL or higher, the correlation was lower (<jats:italic>y</jats:italic>=0.040<jats:italic>x</jats:italic>+38.034 and <jats:italic>r</jats:italic><jats:sup>2</jats:sup>=0.180); these results were evaluated by a quadratic curve, resulting in an increased correlation (<jats:italic>r</jats:italic><jats:sup>2</jats:sup>=0.668).</jats:p></jats:sec><jats:sec><jats:title>Conclusions</jats:title><jats:p>There was a significant correlation between plasma dabigatran concentrations and aPTT. Additionally, in daily clinical practice in Japan, plasma dabigatran concentrations and aPTT reached a peak in the 4‐h post administration range. Considering the pharmacokinetics of dabigatran, aPTT can be used as an index for risk screening for excess dabigatran concentrations in Japanese patients with NVAF.</jats:p></jats:sec>