Half life of amlodipine
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Half-Life of Amlodipine: Pharmacokinetics and Clinical Implications
Introduction to Amlodipine Pharmacokinetics
Amlodipine is a dihydropyridine calcium antagonist widely used for the treatment of hypertension and angina pectoris. Its pharmacokinetic profile is characterized by a notably long half-life, which supports its efficacy in once-daily dosing regimens.
Plasma Half-Life of Amlodipine
Single-Dose Administration
Studies have shown that the plasma half-life of amlodipine varies slightly depending on the mode of administration. When administered intravenously at a single dose of 10 mg, the mean plasma half-life is approximately 34 hours 13. For oral administration of the same dose, the half-life is slightly longer, averaging around 36 hours 13. This extended half-life is a key factor in the drug's ability to maintain therapeutic levels with once-daily dosing.
Repeated Dosing and Steady-State Concentrations
With repeated oral administration, the half-life of amlodipine can extend further. For instance, after 14 days of daily oral dosing at 15 mg, the mean half-life increases to about 45 hours . This prolonged half-life facilitates the accumulation of the drug to steady-state concentrations, typically reached after about one week of consistent dosing 14.
Factors Influencing Half-Life
Age and Hepatic Function
The half-life of amlodipine is influenced by patient-specific factors such as age and liver function. In elderly patients, the half-life is significantly prolonged, averaging around 48 hours compared to younger individuals 56. This is likely due to decreased clearance rates in older adults. Similarly, patients with severe hepatic impairment exhibit a markedly extended half-life, sometimes reaching up to 60 hours 34.
Dosage and Bioavailability
The pharmacokinetic profile of amlodipine remains linear across different dosages, with half-lives reported as 31.2, 33, and 36.8 hours for 2.5 mg, 5 mg, and 10 mg doses, respectively . The drug's bioavailability is relatively high, ranging from 60% to 65%, which supports its effective absorption and prolonged action 49.
Clinical Implications
Hypertension and Angina Management
The long half-life of amlodipine ensures sustained therapeutic effects, making it highly effective for managing hypertension and angina with once-daily dosing. This pharmacokinetic property minimizes fluctuations in plasma drug concentrations, thereby reducing the risk of adverse effects and enhancing patient compliance 810.
Safety and Efficacy
Amlodipine's gradual absorption and extended half-life contribute to its favorable safety profile. The slow onset of action prevents rapid changes in blood pressure, which can trigger reflex tachycardia or other cardiovascular events 910. Additionally, the drug's consistent plasma levels over 24 hours ensure continuous blood pressure control without significant peaks and troughs 810.
Conclusion
Amlodipine's long half-life, ranging from 34 to 60 hours depending on various factors, underpins its effectiveness in once-daily dosing regimens for hypertension and angina. This extended half-life, coupled with high bioavailability and gradual absorption, makes amlodipine a reliable and safe option for long-term cardiovascular management.
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