Evaluation of the chromogenic anti-factor IIa assay to assess dabigatran exposure in geriatric patients with atrial fibrillation in an outpatient setting.

BACKGROUND: Dabigatran etexilate may be underutilized in geriatric patients because of inadequate clinical experience in individuals with severe renal impairment and post-marketing reports of bleeding events. Assessing the degree of anticoagulation may improve the risk:benefit ratio for dabigatran. The aim of this prospective study was to identify whether therapeutic drug monitoring of dabigatran anticoagulant activity using a chromogenic anti-factor IIa assay is a viable option for therapy individualization. METHODS: Plasma dabigatran concentration was assessed in nine patients with nonvalvular atrial fibrillation aged 75 years or older currently receiving dabigatran etexilate for prevention of stroke, using an anti-factor IIa chromogenic assay and HPLC-MS/MS. Trough concentrations were evaluated on two separate occasions to determine intrapatient variation. RESULTS: Blood was collected at 13.1 ± 2.3 h (mean ± SD) post dose from patients prescribed dabigatran etexilate 150 mg twice daily (5/9 patients) or dabigatran etexilate 75 mg twice daily (4/9 patients). Results from the anti-factor IIa chromogenic assay correlated with dabigatran concentrations as assessed by HPLC-MS/MS (r (2)  = 0.81, n = 16). There was no correlation between dabigatran trough values taken at separate visits (r (2)  = 0.002, n = 7). Furthermore, there was no correlation found between the drug concentrations and patients' renal function determined by both creatinine and cystatin-C based equations. None of the patients enrolled in the study were in the proposed on-therapy trough range during at least one visit. CONCLUSION: The chromogenic anti-factor IIa assay demonstrated similar performance in quantifying dabigatran plasma trough concentrations to HPLC-MS/MS. Single measurement of dabigatran concentration by either of two methods during routine visits may not be reliable in identifying patients at consistently low or high dabigatran concentrations.