Norvasc

Active Ingredient & Mechanism of Action

• Active Ingredient: Amlodipine besylate (equivalent to amlodipine free base).
• Mechanism: Norvasc blocks the voltage-gated L-type calcium channels in vascular smooth muscle and cardiac muscle cells, inhibiting the entry of extracellular calcium required for muscle contraction.
  1. Hypertension Control: Vascular smooth muscle cells are exceptionally sensitive to calcium channel blockage. By inhibiting calcium influx, Norvasc promotes systemic arterial vasodilation, lowering peripheral vascular resistance and reducing blood pressure.
  2. Angina Relief: Norvasc reduces cardiac afterload (the force against which the left ventricle must pump), decreasing myocardial work and oxygen consumption. Additionally, it dilates coronary arteries and arterioles, increasing myocardial oxygen delivery—particularly in regions affected by coronary vasospasm.

Dosage Forms & Strengths

• Norvasc 2.5 mg: Recommended for elderly patients, frail individuals, patients with hepatic impairment, or as part of a combination regimen.
• Norvasc 5 mg: Standard initial daily dose for most adults treated for hypertension or angina.
• Norvasc 10 mg: Maximum recommended daily dose, used when target blood pressure or antianginal control is not achieved after 7 to 14 days on the 5 mg dose.

Clinical Indications

• Hypertension: Used alone or in combination with other antihypertensives (such as ACE inhibitors, angiotensin receptor blockers, or diuretics) to reduce blood pressure and lower the risk of stroke and heart attack.
• Chronic Stable Angina: Symptomatic relief and management of patients with chronic stable angina pectoris.
• Vasospastic Angina (Prinzmetal’s or Variant Angina): Treatment of confirmed or suspected coronary artery spasm.
• Angiographically Documented CAD: Reduces the risk of hospitalization for angina and coronary revascularization procedures in patients with CAD without heart failure.

Key Pharmacokinetics

• Absorption & Bioavailability: Gradual oral absorption with peak blood plasma concentrations ($C_{max}$) reached between 6 and 12 hours post-dose. Bioavailability ranges between 64% and 90%. Food does not alter its absorption.
• Duration of Action: Features a long terminal elimination half-life of 30 to 50 hours, providing smooth 24-hour therapeutic coverage with once-daily administration.
• Metabolism & Elimination: Extensively converted in the liver by the CYP3A4 enzyme system into inactive metabolites, with 60% excreted via urine and 10% excreted unchanged.

Administration Guidelines

• Dosage: Taken orally once daily with or without food.
• Consistency: For best results, it should be taken around the same time each day.
• Missed Dose: If a dose is missed by more than 12 hours, skip that dose and resume the normal schedule the next day—do not double up doses.

Safety Profile & Considerations

• Common Side Effects: Peripheral edema (ankle/foot swelling, dose-dependent), dizziness, flushing, fatigue, and palpitations.
• Contraindications: Known hypersensitivity to amlodipine, dihydropyridines, or any component of the formulation.
• Drug Interactions:
  • Simvastatin: Limit simvastatin dosage to a maximum of 20 mg daily when taken concurrently.
  • CYP3A4 Inhibitors: Strong inhibitors (e.g., ketoconazole, clarithromycin) can increase amlodipine exposure, requiring cautious dosing.
  • Immunosuppressants: Co-administration may increase plasma levels of tacrolimus or cyclosporine.

Note: Norvasc is a prescription-only medication. Dose adjustments and treatment plans should strictly follow the directions of a licensed healthcare professional.