Apixaban

Apixaban (Eliquis^®) is an oral factor Xa inhibitor that inhibits thrombin generation, which is critical for clot formation. As an anticoagulant, it is indicated to: 1) reduce the risk of stroke and systemic embolism in patients with nonvalvular atrial fibrillation, 2) prevent deep venous thrombosis (DVT) in patients whom have undergone hip or knee replacement surgery, 3) treat DVT and pulmonary embolism (PE), and 4) reduce the risk of recurrent DVT and PE following initial therapy.¹

No, apixaban has a highly predictable pharmacokinetic profile. Measurement of the drug’s level may be useful, however, when²:

• There is a concern regarding patient compliance and adherence.
• A patient has a very high or low body weight.
• A patient is pregnant.
• There is concurrent administration of a strong inducer of P-glycoprotein and CYP3A4 (eg, phenytoin, carbamazepine, phenobarbital, or St. John’s wort).
• There is concurrent administration of a strong inhibitor of P-glycoprotein and CYP3A4 (eg, azole antimycotics, including ketoconazole, itraconazole, voriconazole, and posaconazole).
• There is concurrent administration of an HIV protease inhibitor (eg, ritonavir).
• There is a thrombotic or hemorrhagic event during therapy.
• A patient has renal or hepatic failure.
• A patient on apixaban therapy is scheduled for surgery.
• A patient is elderly.
• A patient has active cancer.

Because apixaban is administered in fixed doses and does not require routine laboratory monitoring, there are no universally established therapeutic ranges. The steady-state peak and trough ranges for various doses are shown below.

Apixaban is measured using a modified, chromogenic anti-Xa method. The optical density derived from the patient sample is compared to that of calibrators with known apixaban concentration. The results are reported in ng/mL.

The lower limit of detection for the apixaban assay is 30 ng/mL. Trough levels may be below this value; therefore, we suggest samples be collected at the peak (3-4 hours after the last dose).

The assay is not specific for apixaban. It will detect any anti-Xa anticoagulant including unfractionated heparin, low molecular weight heparins (enoxaparin, tinzaparin, dalteparin), rivaroxaban, and fondaparinux.

The coefficient of variation (CV) is less than 6%.

Gross lipemia, icterus, and hemolysis will interfere with apixaban measurement.