What is the half-life of amlodipine?

Half-Life of Amlodipine

Amlodipine has a terminal elimination half-life of approximately 30 to 50 hours, which allows for once-daily dosing and provides steady-state plasma levels after 7-8 days of consecutive administration. 1

Pharmacokinetic Properties

Amlodipine exhibits several distinctive pharmacokinetic characteristics:

• Absorption and bioavailability:

  • Oral bioavailability: 64-90% 1
  • Peak plasma concentrations: 6-12 hours after oral administration 1
  • Food does not alter bioavailability 1

• Distribution:

  • Extensively bound to plasma proteins (approximately 93% in hypertensive patients) 1
  • Large volume of distribution (21 L/kg) 2

• Metabolism and elimination:

  • Extensively metabolized in the liver (about 90% converted to inactive metabolites) 1
  • Biphasic elimination from plasma 1
  • 10% of parent compound and 60% of metabolites excreted in urine 1
  • No significant presystemic or first-pass metabolism 2

Clinical Implications of Long Half-Life

The long half-life of amlodipine provides several clinical advantages:

• Steady plasma concentrations: Small fluctuations (20-25%) between doses with once-daily administration 3
• Gradual onset of effect: Reduces risk of reflex tachycardia 3
• Sustained 24-hour blood pressure control: Particularly effective for controlling morning blood pressure 4
• Slow return to baseline after discontinuation: Blood pressure gradually returns to baseline over 7-10 days without evidence of rebound effect 3

Special Populations

The pharmacokinetics of amlodipine may be altered in certain patient populations:

• Elderly patients: Decreased clearance with resulting increase in AUC by 40-60% 1
• Hepatic insufficiency: Decreased clearance with resulting increase in AUC by 40-60% 1
• Renal impairment: Pharmacokinetics not significantly influenced; usual initial dose can be used 1
• Heart failure: Increased AUC by 40-60% in patients with moderate to severe heart failure 1

Pharmacokinetic Considerations in Adherence Testing

In the context of medication adherence testing, amlodipine's long half-life has important implications:

• Due to its slow clearance (half-life 34-50 hours), amlodipine may remain detectable in biological samples for extended periods 5
• A patient could be taking amlodipine sporadically but still test positive up to a week after the last ingestion 5
• This contrasts with medications having shorter half-lives (e.g., hydrochlorothiazide at 6.4 hours) 5

The long half-life of amlodipine contributes to its suitability for once-daily dosing regimens, potentially improving medication adherence and providing consistent 24-hour blood pressure control.