apixaban

Mechanism: Apixaban directly and selectively inhibits both free and clot-bound factor Xa, preventing the conversion of prothrombin to thrombin, thereby reducing thrombin generation and thrombus formation. It does not require antithrombin as a cofactor (unlike heparin).

Pharmacokinetics: Administered orally with predictable pharmacokinetics, allowing for fixed dosing without routine monitoring. It has a rapid onset of action (peak effect in 3-4 hours) and a half-life of about 12 hours, typically dosed twice daily. Elimination is via multiple pathways including renal (~27%), hepatic metabolism (CYP3A4), and direct intestinal excretion, making it relatively safer in renal impairment compared to other DOACs like dabigatran.

Clinical Use: Part of the direct oral anticoagulant (DOAC) class along with rivaroxaban, edoxaban, and betrixaban. Indications include: stroke/systemic embolism prevention in nonvalvular AFib, treatment and secondary prevention of DVT/PE, and VTE prophylaxis after hip/knee arthroplasty. Apixaban has shown non-inferiority to warfarin with lower rates of major bleeding, particularly intracranial hemorrhage.

Contraindications/Cautions: Avoid in patients with mechanical heart valves or moderate-to-severe mitral stenosis (must use warfarin instead). Dose reduction required in patients with specific combinations of age ≥80, body weight ≤60 kg, or serum creatinine ≥1.5 mg/dL.

Reversal: Andexanet alfa is a specific reversal agent (a recombinant modified factor Xa decoy protein) for life-threatening bleeding; activated charcoal may help if taken within a few hours of ingestion. Unlike warfarin, apixaban's effect cannot be reliably reversed with vitamin K or FFP.

Monitoring: No routine monitoring required, though anti-Xa assays can be used to assess drug levels in specific clinical scenarios (e.g., before urgent surgery, suspected overdose).

Drug Interactions: Strong CYP3A4/P-glycoprotein inhibitors (e.g., ketoconazole, ritonavir) increase apixaban levels; strong inducers (e.g., rifampin, phenytoin) decrease levels.