Half-Life of Amlodipine Benzoate
The half-life of amlodipine is 34-50 hours, making it one of the longest-acting calcium channel blockers available. 1
Pharmacokinetic Profile of Amlodipine
Amlodipine has several distinctive pharmacokinetic properties that contribute to its clinical utility:
- Elimination half-life: 34-50 hours 1, with some sources reporting 35-50 hours 2 or 36-45 hours 3
- Absorption: Slow absorption after oral administration, with peak plasma concentrations occurring 6-8 hours after dosing 4
- Bioavailability: High oral bioavailability (60-80%) 4
- Metabolism: Extensively metabolized by the liver 5
- Clearance: Low renal clearance (7 mL/min/mg) 2
- Steady state: Accumulates to steady-state with once-daily administration over 1-1.5 weeks 4
- Plasma concentration fluctuation: Minimal (20-25%) between doses with once-daily dosing 4
Clinical Implications of Amlodipine's Long Half-Life
The extended half-life of amlodipine provides several clinical advantages:
- Sustained blood pressure control: Maintains antihypertensive effect for more than 24 hours following a single dose 2
- Forgiveness factor: Blood pressure control is maintained even when a dose is missed, providing protection in cases of incidental noncompliance 2
- Once-daily dosing: The long half-life allows for convenient once-daily administration 3
- Smooth action: Gradual onset of effect without reflex tachycardia 4
- Reduced blood pressure variability: The long half-life contributes to reduced fluctuations in blood pressure 2
Special Considerations
- Hepatic impairment: The plasma elimination half-life increases to 56 hours in patients with impaired hepatic function, requiring slower dose titration in these patients 5
- Medication adherence monitoring: Due to its long half-life, amlodipine may remain detectable in biological samples for extended periods, which can affect interpretation of adherence testing. A patient may be dosing sporadically but still test positive up to a week after the last ingestion 1
- Discontinuation: After stopping amlodipine, blood pressure returns to baseline gradually over 7-10 days, without evidence of rebound effect 4
Comparative Half-Lives Among Calcium Channel Blockers
Amlodipine's half-life is significantly longer than other calcium channel blockers, which contributes to its superior 24-hour blood pressure control:
- Amlodipine: 34-50 hours 1
- Felodipine: Shorter half-life (comparative study showed amlodipine provided better nighttime blood pressure control) 6
- Nifedipine: Much shorter half-life (comparative studies show amlodipine's advantages in 24-hour coverage) 3
The long half-life of amlodipine makes it particularly suitable for patients who may occasionally miss doses and for those requiring stable 24-hour blood pressure control.