amlodipine besylate

FDA-Approved Indications:

Hypertension (adults and pediatric patients ≥6 years):

• Treatment of hypertension to reduce blood pressure and lower the risk of cardiovascular events
• Can be used as monotherapy or in combination with other antihypertensives (e.g., ACE inhibitors, ARBs, thiazides)
• Pediatric use: approved for children ≥6 years; dose 2.5–5 mg once daily

Coronary Artery Disease (CAD):

• Chronic stable angina: Reduces frequency of angina episodes and nitroglycerin use
• Vasospastic angina (Prinzmetal's or variant angina): Blocks coronary artery spasm; confirmed in controlled trials
• Angiographically documented CAD without heart failure or EF <40%: Reduces risk of hospitalization for angina and coronary revascularization procedures (CAMELOT trial)

Guideline-Recommended Uses (off-label but strongly supported):

• Hypertension with CKD: Preferred CCB in patients with proteinuric CKD when combined with RAAS blockade
• Raynaud's phenomenon: Reduces frequency and severity of vasospastic episodes
• Hypertension in pregnancy (2nd/3rd trimester): Considered relatively safe; used when methyldopa or labetalol are not tolerated
• Hypertension with peripheral artery disease: Preferred over beta-blockers due to vasodilatory properties

Dosing by Indication:

Hepatic Dose Adjustment:

• Mild-to-moderate hepatic impairment: Start at 2.5 mg once daily (reduced metabolism increases exposure)
• Severe hepatic impairment: Use with caution; start at 2.5 mg; no specific dose recommendation

Renal Dose Adjustment:

• No dose adjustment required for any degree of renal impairment
• Amlodipine is not removed by hemodialysis

Administration:

• Take with or without food
• Can be taken at any time of day; consistency is more important than timing
• If a dose is missed, take as soon as remembered; skip if almost time for next dose; do not double up
• Available as tablets (2.5 mg, 5 mg, 10 mg) and oral suspension (1 mg/mL — Katerzia, Norliqva)

Mechanism of Action — L-Type Calcium Channel Blockade

Amlodipine is a dihydropyridine (DHP) calcium channel blocker that selectively inhibits the influx of calcium ions through voltage-gated L-type calcium channels in vascular smooth muscle and cardiac muscle cells.

Step-by-step mechanism:

1. L-type calcium channel blockade: Amlodipine binds to the alpha-1 subunit of L-type (long-lasting) voltage-gated calcium channels in vascular smooth muscle cells. This binding is highly selective — amlodipine has approximately 1,000-fold greater affinity for vascular smooth muscle than for cardiac muscle.

2. Reduced intracellular calcium: By blocking calcium entry, amlodipine reduces intracellular calcium concentrations in vascular smooth muscle. Calcium is required for the activation of myosin light chain kinase (MLCK), which drives smooth muscle contraction.

3. Vasodilation and blood pressure reduction: Reduced intracellular calcium leads to smooth muscle relaxation and peripheral arterial vasodilation. This decreases peripheral vascular resistance (afterload), lowering systolic and diastolic blood pressure. Unlike ACE inhibitors and ARBs, amlodipine does not affect the RAAS system.

4. Anti-anginal effects: In the coronary circulation, amlodipine dilates coronary arteries and arterioles, increasing oxygen supply to the myocardium. It also reduces myocardial oxygen demand by decreasing afterload (rate-pressure product). In vasospastic angina, it prevents calcium-mediated coronary artery spasm.

Key pharmacological properties:

• Gradual onset: Amlodipine has a unique slow rate of association with and dissociation from the calcium channel receptor (due to its ionized form at physiologic pH, pKa 8.6), resulting in a gradual onset and long duration of action — no reflex tachycardia
• Vascular selectivity: ~1,000× more selective for vascular vs. cardiac calcium channels; minimal negative inotropic effect at therapeutic doses
• No reflex tachycardia: Unlike nifedipine IR, amlodipine's gradual vasodilation does not trigger baroreceptor-mediated sympathetic activation

Clinical trial evidence:

• ALLHAT (2002): Amlodipine was equivalent to lisinopril and chlorthalidone in preventing fatal coronary heart disease and nonfatal MI in 33,357 high-risk hypertensive patients
• CAMELOT (2004): Amlodipine 10 mg reduced cardiovascular events by 31% vs. placebo in patients with CAD and normal blood pressure (n=1,318)
• ASCOT-BPLA (2005): Amlodipine-based therapy reduced stroke by 23%, cardiovascular events by 16%, and all-cause mortality by 11% vs. atenolol-based therapy (n=19,257)

Key Drug Interactions:

Note on peripheral edema: The edema caused by amlodipine is due to arteriolar vasodilation (not fluid retention) and does NOT respond to diuretics. Adding a diuretic will not resolve amlodipine-induced edema.

Pregnancy:

• Category C (1st trimester); limited human data
• Animal studies show embryotoxicity at high doses
• Use only if benefit outweighs risk; amlodipine is sometimes used in 2nd/3rd trimester for hypertension in pregnancy when methyldopa or labetalol are not tolerated
• Neonatal hypotension has been reported with maternal use near delivery

Breastfeeding:

• Amlodipine is excreted in breast milk (infant dose ~4% of maternal dose)
• Monitor infant for hypotension, somnolence, and poor feeding
• Consider benefits of breastfeeding vs. risk to infant

Pediatric Use:

• Approved for hypertension in children ≥6 years
• Dose: 2.5–5 mg once daily (not to exceed 5 mg/day)
• Safety and efficacy not established in children <6 years
• Pediatric pharmacokinetics similar to adults

Geriatric Use:

• Elderly patients may have increased amlodipine exposure (longer half-life ~65 hours vs. 50 hours in younger adults)
• Start at 2.5 mg once daily in elderly patients
• Monitor for peripheral edema and hypotension
• No dose adjustment required for renal impairment

Hepatic Impairment:

• Extensive hepatic metabolism; start at 2.5 mg in mild-to-moderate impairment
• No data in severe hepatic impairment; use with caution

Renal Impairment:

• No dose adjustment required; amlodipine is not dialyzable