Half-life of Nifedipine
Nifedipine has a short half-life of approximately 2 hours in its immediate-release formulation, while extended-release formulations have a longer half-life of approximately 7 hours. 1
Pharmacokinetic Properties of Nifedipine
Immediate-Release Formulation
- Half-life: Approximately 2 hours 1
- Absorption: Almost completely absorbed from the gastrointestinal tract 2
- Bioavailability: 56% to 77% (due to presystemic metabolism) 2
- Peak plasma concentration: Reached within 30-60 minutes after oral administration 2
- Elimination: Biphasic with initial alpha-phase half-life of about 13 minutes and beta-phase half-life of about 1.26 hours 2
Extended-Release Formulation
- Half-life: Approximately 7 hours 1
- Peak plasma concentration: Occurs at about 2.5-5 hours post-dose with a second small peak at 6-12 hours 1
- Metabolism: Extensively metabolized via cytochrome P450 3A4 system 1
- Excretion: 60-80% of the dose excreted in urine as water-soluble inactive metabolites; less than 0.1% excreted unchanged in urine; remainder excreted in feces 1
Clinical Implications of Half-Life
Dosing Frequency
- Immediate-release nifedipine: Requires multiple daily dosing due to short half-life 3
- Extended-release formulations: Allow for once-daily dosing 1
Safety Considerations
- Immediate-release nifedipine is not recommended for hypertensive crisis or unstable angina/NSTEMI except with concomitant beta blockade due to risk of adverse cardiovascular events 3
- The short half-life of immediate-release nifedipine can lead to rapid fluctuations in blood pressure, potentially causing reflex tachycardia 4
- Extended-release formulations provide more stable plasma concentrations, reducing the risk of adverse effects 5
Stability Considerations
- Nifedipine is unstable when stored at room temperature (25°C) for more than 1 day 3
- For laboratory testing purposes, samples containing nifedipine should be stored at -20°C for stability 3
Comparison with Other Calcium Channel Blockers
| Drug | Half-Life | Duration of Action |
|---|---|---|
| Nifedipine (immediate-release) | ~2 hours | Short |
| Nifedipine (extended-release) | ~7 hours | Long |
| Amlodipine | 34-50 hours | Long |
| Diltiazem | Variable (short for immediate-release, long for extended-release) | Short to Long |
| Verapamil | Variable (short for immediate-release, long for extended-release) | Short to Long |
The relatively short half-life of nifedipine compared to other calcium channel blockers like amlodipine (34-50 hours) explains why immediate-release nifedipine requires multiple daily dosing while amlodipine can be administered once daily 3.
Understanding the half-life of nifedipine is critical for appropriate dosing, patient adherence, and minimizing adverse effects related to rapid fluctuations in drug concentration.