Nifedipine

Active Ingredient & Mechanism of Action

• Active Ingredient: Nifedipine.
• Mechanism: Nifedipine selectively blocks the transmembrane influx of calcium ions into arterial smooth muscle cells and cardiac muscle:
  1. Peripheral Vasodilation: By inhibiting calcium influx, it relaxes systemic arterial smooth muscle, lowering total peripheral resistance and decreasing systemic blood pressure.
  2. Coronary Vasodilation & Afterload Reduction: It dilates main coronary arteries and arterioles, improving myocardial oxygen supply. It also reduces the afterload against which the heart pumps, decreasing cardiac workload and oxygen consumption to relieve angina.

Available Strengths & Dosage Forms

• Extended-Release (ER/XL) Tablets (e.g., Adalat CC, Procardia XL): Standard strengths include 30 mg, 60 mg, and 90 mg. Designed for once-daily dosing to manage hypertension and angina smoothly over 24 hours.
• Immediate-Release (IR) Capsules (e.g., Procardia): Standard strengths include 10 mg and 20 mg. Used primarily for angina management (3 to 4 times daily).

Clinical Indications

• Essential Hypertension: Managed exclusively with extended-release formulations.
• Chronic Stable Angina & Vasospastic Angina (Prinzmetal’s Angina): Used alone or in combination with beta-blockers.
• Raynaud’s Phenomenon (Off-Label / Regional Use): Helps prevent cold-induced arterial spasms in digits.
• Tocolysis / Hypertension in Pregnancy (Off-Label): Used under strict specialist supervision to suppress preterm labor or manage severe gestational hypertension/preeclampsia.

Key Pharmacokinetics

• Absorption: Rapidly and almost completely absorbed from the gastrointestinal tract.
• Bioavailability & Food: Significant first-pass metabolism; extended-release forms are best taken on an empty stomach or as consistently directed.
• Half-Life & Elimination: Short half-life ($\sim 2\text{–}5\text{ hours}$) for immediate-release forms, necessitating extended-release matrix technology for once-daily coverage. Metabolized almost entirely by the liver (CYP3A4) and excreted via urine.

Administration Guidelines

• Extended-Release Tablets: Must be swallowed whole once daily with water. Do not crush, split, chew, or break.
• Dietary Restrictions: Avoid grapefruit and grapefruit juice while taking nifedipine, as grapefruit inhibits CYP3A4 metabolism, significantly increasing drug levels and toxicity risk.

Safety Profile & Considerations

• Common Side Effects: Peripheral edema (lower leg/ankle swelling, dose-dependent), headache, dizziness, flushing, nausea, and reflex tachycardia.
• Contraindications:
  • Known hypersensitivity to nifedipine or other dihydropyridines.
  • Cardiogenic shock or recent acute myocardial infarction (within 2–4 weeks).
  • Severe aortic stenosis.
• Key Precautions & Interactions:
  • Strong CYP3A4 Inhibitors/Inducers: Drugs like ketoconazole, clarithromycin, or rifampin alter nifedipine blood concentrations significantly.
  • Severe GI Stenosis: Extended-release formulations with non-deformable shells should be used with caution in patients with severe gastrointestinal narrowing.

Note: Nifedipine is a prescription-only medication. Treatment, formulation selection, and dose adjustments must strictly follow the directions of a licensed healthcare professional.