Five Half-Lives of Eliquis Equals 5 Doses
In a patient with normal kidney function taking standard-dose Eliquis (apixaban) 5 mg twice daily, five half-lives equals approximately 5 doses (2.5 days).
Pharmacokinetic Basis
The calculation is straightforward based on apixaban's elimination half-life:
- Apixaban has a half-life of approximately 12 hours in patients with normal renal function 1
- The European Heart Journal guidelines specify the half-life range as 9-14 hours 2
- Five half-lives = 5 × 12 hours = 60 hours (2.5 days) 2, 1
Dose Conversion
Since Eliquis is dosed twice daily (every 12 hours):
- Each dosing interval = 12 hours = 1 half-life 2
- 60 hours ÷ 12 hours per dose = 5 doses 2
- This means skipping 4 doses after the last dose taken 2
Clinical Context for Five Half-Lives
Five half-lives represents the time needed to eliminate approximately 97% of the drug from the body 2:
- After 1 half-life: 50% remains
- After 2 half-lives: 25% remains
- After 3 half-lives: 12.5% remains
- After 4 half-lives: 6.25% remains
- After 5 half-lives: 3.125% remains 2
The ACC guidelines use this principle when managing perioperative anticoagulation, noting that 4-5 half-lives corresponds to minimal residual anticoagulant effect (3-6%) 2.
Impact of Renal Function
This calculation assumes normal kidney function (CrCl ≥80 mL/min) 2:
- Moderate renal impairment (CrCl 30-49 mL/min): Half-life extends to approximately 18 hours, so five half-lives = 90 hours = 7-8 doses 2
- Severe renal impairment (CrCl 15-29 mL/min): Half-life extends to approximately 27 hours 2
- Renal excretion accounts for only 27% of apixaban clearance, making it less affected by renal dysfunction than dabigatran 2, 1
Perioperative Management Application
The Blood journal guidelines for elective procedures recommend 2:
- High bleeding risk surgery in normal renal function: Last dose 3 days before surgery (skip 4 doses) = approximately 4-5 half-lives 2
- Low bleeding risk surgery in normal renal function: Last dose 2 days before surgery (skip 2 doses) = approximately 2-3 half-lives 2
Important caveat: The standard-dose apixaban (5 mg twice daily) applies to most patients, but dose reduction to 2.5 mg twice daily is indicated when at least 2 of the following are present: age ≥80 years, body weight ≤60 kg, or serum creatinine ≥1.5 mg/dL 2, 1. The half-life remains approximately 12 hours regardless of dose 1.