Overview
Apixaban is a direct oral anticoagulant (DOAC) used to prevent and treat blood clots. It is highly effective in reducing the risk of stroke and systemic embolism in patients with nonvalvular atrial fibrillation, and is also used for the treatment and prevention of deep vein thrombosis (DVT) and pulmonary embolism (PE).

Mechanism of Action
It acts as a highly selective, reversible, and direct inhibitor of Factor Xa, a crucial enzyme in the blood coagulation cascade. By inhibiting Factor Xa, apixaban prevents the conversion of prothrombin to thrombin, thereby inhibiting the formation of fibrin clots. Unlike warfarin, it does not require a cofactor (like antithrombin III) for its activity.

Dosage and Administration
For stroke prevention in atrial fibrillation, the standard dose is 5 mg twice daily. The dose is reduced to 2.5 mg twice daily for patients meeting at least two of the following criteria: age ≥80 years, body weight ≤60 kg, or serum creatinine ≥1.5 mg/dL. For treating DVT/PE, a higher initial dose (10 mg twice daily for 7 days) is followed by a maintenance dose of 5 mg twice daily. Routine coagulation monitoring (like INR) is not required.

Side Effects
The most significant side effect is an increased risk of bleeding, which can range from minor bruising to severe, life-threatening internal bleeding (e.g., gastrointestinal or intracranial hemorrhage). It generally has a lower risk of major bleeding compared to warfarin.

Contraindications
It is contraindicated in patients with active pathological bleeding, severe hepatic impairment associated with coagulopathy, or a known hypersensitivity to the drug. It should be discontinued prior to invasive procedures to minimize bleeding risk.

Pregnancy and Lactation
Use during pregnancy is not recommended as there is limited data on its safety, and it may increase the risk of maternal bleeding. It is excreted in animal milk, so women should not breastfeed while taking apixaban.