A 72-year-old man with a history of nonvalvular atrial fibrillation (AF) and hypertension presents to the ER after an episode of hematochezia. He is prescribed dabigatran 150 mg twice daily for his AF and took his evening dose 2 hours prior to presentation. His initial exam reveals vital signs of BP 120/55, HR 105, RR 14 and bright red stool on rectal exam. His hemoglobin is 8.1 g/dL, down from 12.0 g/dL one month ago. He has normal renal function. How should you manage his gastrointestinal bleeding?
Direct oral anticoagulants (DOACs) consist of two classes of drugs: oral factor Xa inhibitors (apixaban, edoxaban, and rivaroxaban) and direct thrombin inhibitors (dabigatran). They have gained substantial popularity since their commercial introduction in 2010, and are now Food and Drug Administration approved for the treatment of atrial fibrillation (AF) and venous thromboembolism (VTE) in noncancer patients. DOAC use will likely increase given favorable safety profiles, reliable pharmacokinetics, and recent guidelines recommending their use over vitamin K antagonists (VKAs) for treatment of VTE in noncancer patients.1
A primary concern about the routine use of DOACs has been the lack of commercially available direct reversal agents. Unlike warfarin, which has an effective rapid antidote, no direct reversal agent is available for Xa inhibitors, and only recently has there been FDA approval for idarucizumab, a direct thrombin inhibitor reversal drug. Therefore, clinicians are often left wondering how to manage bleeding episodes in patients receiving DOACs.
What is the risk of bleeding for patients taking DOACs?
DOACs carry a low but significant risk of bleeding, including life-threatening bleeding. There is now robust data from over 100,000 patients in randomized clinical trials of nonvalvular AF and VTE comparing the risk of major and fatal bleeding between DOACs and VKAs.2 These trials reveal an annual major bleeding rate of 2%-4% in patients with AF and 1%-2% in patients with VTE taking DOACs.
Importantly, DOACs were found to carry a statistically lower risk of major and fatal bleeding than VKAs. Patients taking DOACs have a relative risk of major bleeding of 0.72, compared with VKAs, and a RR of fatal bleeding of 0.53. Additionally, the case fatality rate for major bleeding episodes was 7.6% for DOACs versus 11.0% for warfarin, despite not having an available antidote for DOACs in these trials.3 Although there is an increased risk of bleeding from DOACs, the rates of major bleeding and of serious complications from bleeding are lower than with warfarin.
How long does the effect of a DOAC last?
A significant advantage of DOACs over VKAs in the setting of bleeding is their shorter half-lives, which range from a low estimate of 5 hours for rivaroxaban to a high estimate of 17 hours for dabigatran4-8 (Table 1). Given that it takes 4-5 half-lives for a drug to be functionally eliminated, coagulation typically normalizes in patients taking DOACs within 1-3 days, compared with 3-5 days for warfarin. All DOACs have significant renal clearance, and renal failure will prolong the duration of anticoagulation. For patients who are taking DOACs and present with bleeding, it is important to assess their renal function.
Are coagulation tests helpful when assessing the effect of DOACs?
Prothrombin time (PT/INR) and activated partial thromboplastin time (aPTT) should be measured in all patients presenting with significant bleeding, whether or not the patient is taking a DOAC. PT and aPTT are commonly elevated for patients taking direct thrombin inhibitors and Xa inhibitors. Although a prolonged PT and/or aPTT can be useful in determining if the anticoagulant effect from DOACs is still present, normal values of these tests do not rule out an anticoagulant effect in patients taking DOACs.9,10 Thrombin Time (TT) is a widely available test with quick results, and a normal value rules out the therapeutic effect of dabigatran. Finally, the anti–factor Xa assay is a sensitive test for Xa inhibitors, but requires calibration to the DOAC of interest in order to be reliable. Clinicians should consult with their institution’s laboratory prior to using an anti–factor Xa level to test the anticoagulant effect of a specific DOAC. Repeat coagulation testing may be useful in some clinical circumstances, especially if a patient has renal impairment.
Are there reversal agents for DOACs?
In October 2015, the FDA approved idarucizumab, a monoclonal antibody fragment that binds dabigatran with much greater affinity than thrombin, thus quickly reversing the effect of the direct thrombin inhibitor. FDA approval came in response to an interim analysis of an ongoing open-label trial, RE-VERSE AD.11 This study enrolled 90 adults with major bleeding or need for an emergency procedure taking dabigatran to receive idarucizumab (2.5 g in 50 mL rapid infusion dose given twice less than 15 minutes apart for a total of 5 g). Idarucizumab immediately reversed the effect of dabigatran on clotting tests in 88%-98% of the patients. For patients with major bleeding, the median time for bleeding cessation was 11.4 hours. One thrombotic event was reported within 72 hours of drug administration. Therefore, in patients taking dabigatran with an elevated TT, idarucizumab may be used if the bleeding is life threatening and refractory to initial supportive measures.