Background: Apixaban, a direct factor Xa inhibitor, has been shown to be at least as safe and probably more effective than dalteparin for the treatment of Cancer Associated venous Thrombosis (CAT), as reported in the ADAM-VTE trial. In the latter study however, only 10.7% of patients weighed less than 60Kg while hospitals in other countries may treat a significantly higher percentage of low-weight individuals. At our CAT Clinic 40% of individuals weigh under 60Kg and 25.4% under 55Kg. Lower weight-based doses are supported by cancer-specific studies such as for edoxaban (Hokusai-VTE Cancer) as well as rivaroxaban in childhood VTE (EINSTEIN Jr).

Aims: We routinely treat patients with CAT weighing between 60-120Kg with full-dose apixaban and those bellow 60Kg receive full-dose anticoagulation for the first month and decrease to 2.5 mg BID thereafter. We sought to determine whether low-weight individuals are being similarly anticoagulated as determined by apixaban plasma levels.

Methods: Apixaban plasma through levels were determined after a minimum of 7 days on steady dose treatment.

Results: Full-dose anticoagulation in low weight patients (40-60Kg) doubled the median through apixaban plasma levels (median: 229, min/max: 70-578 p:0.67) while those receiving 2.5 mg BID attained similar plasma levels as compared to those patients over 60Kg given full dose anticoagulation (median: 82 min/max:12-359 versus median:106 min/max:13-381, respectively, p:0.723). We found an inverse relation between apixaban levels and albumin (p:0.001).

Conclusions: Patients with CAT and low-weight may be underrepresented in published studies and may be over-anticoagulated with regular therapeutic-dose apixaban. Prospective studies assessing thrombotic and bleeding risk in these individuals are warranted.

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ISTH Congress Abstracts - https://abstracts.isth.org/abstract/apixaban-levels-in-cancer-associated-thrombosis-in-low-weight-individuals/