Anticoagulants and Recurrent Thrombosis

Anticoagulants and Recurrent Thrombosis Posted By:

The other day a student asked me, "If a patient is taking a blood thinner for a previous venous thromboembolism (VTE), is it still possible for them to get a blood clot?" Easy answer: yes. Medications such as aspirin, warfarin (Coumadin, Jantoven), dabigatran (Pradaxa), rivaroxaban (Xarelto), apixaban (Eliquis), and low-molecular-weight heparin (LMWH) significantly decrease the risk of blood clotting but will not decrease the risk to zero. Additionally, despite being on therapeutic doses of anticoagulants, patients can still develop recurrent pulmonary embolism (PE), which is appropriately termed "anticoagulation failure." The rate of recurrent PE is up to 4% with LMWH, and 2% to 4% with vitamin K antagonists (VKA) such as warfarin.

Anticoagulants must be taken exactly as directed to work safely and effectively. Known causes of recurrent VTE on therapeutic anticoagulation include occult neoplasm (particularly myeloproliferative neoplasms), active antiphospholipid antibody syndrome (APLAS), and inconsistent medication adherence. Interactions with other medications, food, and alcohol are common with warfarin. These interactions are less so with the newer anticoagulants.

Carefully review details of patient compliance when assessing recurrent VTE symptoms. One study reported that 17% of patients were noncompliant in the first 3 months of treatment, and compliance declined further over the next 6 to 12 months. For patients receiving direct oral anticoagulants (DOACs) who have prolonged ED stays for observation or admission, ensure that you prescribe DOACs according to the patient's dosing schedule, in order to prevent the potential for recurring VTE. If you are in the ED and the patient has a hemodynamically or clinically significant recurrent VTE, begin treatment with parenteral unfractionated heparin (UFH) or LMWH and obtain hematology consultation if available.

Long-term management strategies include changing the patient to a different anticoagulant (ie, DOAC to warfarin or warfarin to LMWH), increasing the anticoagulation to higher doses, or targeting a higher therapeutic international normalized ratio (INR) for warfarin. These considerations are best managed by a hematologist.