Incomplete responses to the recommended dose of idarucizumab: a systematic review and pharmacokinetic analysis.

Dabigatran, a direct thrombin inhibitor, is 80% renally eliminated and demonstrates multi-compartmental pharmacokinetics. Idarucizumab is a monoclonal antibody that reverses dabigatran-induced anticoagulation and displays single compartment pharmacokinetics, with a smaller volume of distribution and shorter elimination half-life than dabigatran. These differences in pharmacokinetics mean that redistribution of dabigatran from peripheral compartments can occur after idarucizumab has been eliminated, resulting in rebound in the dabigatran plasma concentration and treatment failure. Clinical experience notes failure of a single idarucizumab 5 g dose to fully reverse coagulopathy in certain patients. To identify factors predisposing to an incomplete response to the standard idarucizumab 5 g dose. A systematic literature search in PubMed using terms "dabigatran" and "idarucizumab" covering 2015 to October 2019 identified 387 entries. Titles and abstracts were screened initially, followed by full text review and data extraction from 97 eligible articles. Data extracted included clinical information, dabigatran concentrations, coagulation results, idarucizumab dosage and patient outcomes. Pharmacokinetic simulations were conducted using a two-compartment model to predict the likelihood that acute or chronic kidney disease will contribute to an incomplete reversal of dabigatran-induced anticoagulation. Of 240 published cases receiving idarucizumab, 33 reported dabigatran concentration rebound, within a median time of 22 h. From 231 cases reporting idarucizumab dose, 10 received repeated administration due to a rebound in dabigatran concentrations. Baseline dabigatran concentrations >228 ng/mL were more likely to experience a rebound post-idarucizumab to >30 ng/mL (detectable). For baseline dabigatran >488 ng/mL, the concentration rebounded to >75 ng/mL (therapeutic). Idarucizumab is expected to neutralise a maximum plasma dabigatran concentration of 980 ng/mL, but most likely a lesser amount. Pharmacokinetic modelling suggests, for patients taking dabigatran 150 mg twice daily, an incomplete response to 5 g idarucizumab is predicted after approximately 72 h dosing when GFR less than 30 mL/min (25% of normal), and after 36 h with severely impaired renal function (GFR 6 mL/min; GFR 5% of normal). Idarucizumab has neutralised dabigatran following deliberate self-poisoning with dabigatran in a limited number of cases, even in the absence of bleeding. There are insufficient data regarding the use of idarucizumab as part of standard supportive care in this context. The dilute thrombin time can be used to determine the dabigatran concentration, but other more standard coagulation assays are less precise. A normal aPTT largely excludes dabigatran. We suggest performing coagulation assays and dabigatran concentrations every 6 h for a minimum of 36 h after idarucizumab administration to detect a rebound in dabigatran. This is particularly necessary in patients with glomerular filtration rate <30 mL/min or those with a plasma dabigatran concentration exceeding approximately 500 ng/mL. If a rebound in dabigatran is noted, then repeat administration of idarucizumab 5 g can be considered for reversal of recurrent coagulopathy if clinically indicated. The use of idarucizumab for reversal of dabigatran is complex and requires consideration of clinical circumstances and laboratory investigations. Monitoring post-idarucizumab may be required in acute or chronic kidney disease to detect a rebound in dabigatran concentration and the need for additional doses of idarucizumab.