Amlodipine

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amlodipine hypertension

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I now have everything needed for a thorough answer. Here is a complete pharmacological profile of amlodipine:

Amlodipine

Structures of the three major calcium channel blocker classes. Amlodipine (right) bears a dihydropyridine ring, an aminoethoxymethyl side chain, and a 2-chlorophenyl substituent.

Class & Chemistry

Amlodipine is a dihydropyridine (DHP) calcium channel blocker (CCB). Among the clinically used CCBs - which also include the phenylalkylamine verapamil and the benzothiazepine diltiazem - the DHPs are structurally and pharmacodynamically distinct. Amlodipine is unique within the DHP subclass because it appears to bind to both dihydropyridine and non-dihydropyridine sites on the L-type Ca²⁺ channel, producing peripheral arterial vasodilation without significant activation of the sympathetic nervous system (SNS).

Mechanism of Action

Ca²⁺ channel blockers bind to the α-subunit of the L-type (voltage-gated, "slow") Ca²⁺ channel, reducing Ca²⁺ flux into:

Vascular smooth muscle - leads to relaxation, arterial dilation, and reduced peripheral vascular resistance (PVR)
Cardiac myocytes - negative inotropic effect (less prominent with DHPs)
SA/AV nodal cells - slowed conduction (minimal with amlodipine vs. verapamil/diltiazem)

Because amlodipine acts primarily on vascular calcium channels, it functions almost entirely as an arteriolar vasodilator with minimal direct cardiac conduction effects. This contrasts sharply with verapamil (strongest negative inotrope + chronotrope) and diltiazem (intermediate).

Pharmacokinetics

Parameter	Value
Bioavailability	~64-90% (almost complete oral absorption)
Time to peak (Tmax)	6-12 hours
Plasma protein binding	~93%
Elimination half-life (t½)	30-50 hours (prolonged in elderly)
Onset of clinical effect	~24 hours
Steady state	Achieved after 7-8 days of continuous dosing
Metabolism	~90% hepatic (CYP3A4); 10% excreted unchanged
Excretion	Primarily urine (metabolites); no dose adjustment needed in renal impairment
Hepatic insufficiency	Reduce dose; 2.5 mg/day starting dose

The exceptionally long t½ (30-50 h) is what enables once-daily dosing and contributes to smooth, sustained blood pressure control with minimal peak-trough fluctuation. The hypotensive effect can persist up to 5 days after stopping the drug.

Indications

Hypertension - first-line agent, alone or in combination; particularly effective combined with an ACE inhibitor or ARB. The ASCOT trial showed amlodipine + perindopril was superior to atenolol + hydrochlorothiazide for cardiovascular outcomes. The ACCOMPLISH trial showed amlodipine + benazepril was superior to benazepril + HCTZ.
Stable angina (effort-induced) - reduces myocardial oxygen demand by decreasing afterload via arteriolar dilation
Vasospastic (variant/Prinzmetal) angina - directly relaxes coronary arteries, relieving spasm

Dosing

Population	Dose
Adults	5-10 mg once daily (start 5 mg, max 10 mg)
Hepatic insufficiency	2.5 mg once daily
Children 6-17 years	2.5 mg once daily (max 10 mg/day)
Children <6 years	0.1 mg/kg/dose once-twice daily (max 0.6 mg/kg/24h up to 5 mg/24h)

Allow 5-7 days before dose adjustments given the drug's gradual onset and long t½.

Adverse Effects

Most are dose-related:

Peripheral (ankle) edema - the most common adverse effect; caused by precapillary arteriolar dilation and "capillary leakage" rather than fluid retention, making it less responsive to diuretics. Combining with an ACE inhibitor/ARB reduces this via postcapillary venodilation.
Flushing - due to peripheral vasodilation
Dizziness / headache
Palpitations / reflex tachycardia - baroreceptor-mediated sympathetic activation from falling PVR (generally mild with amlodipine due to slow onset)
Fatigue, nausea, somnolence, abdominal pain

Unlike verapamil and diltiazem, amlodipine does not cause significant bradycardia, AV block, or worsen heart failure (it is safe in HFrEF at standard doses, unlike non-DHP CCBs).

Key Drug Interactions

CYP3A4 inhibitors (azole antifungals such as fluconazole and ketoconazole; HIV protease inhibitors) - increase amlodipine levels; use with caution
Cyclosporine, tacrolimus, simvastatin - amlodipine may increase plasma levels and toxicity of these drugs
Beta-blockers - combination is generally safe and used in angina (no risk of AV block unlike with verapamil or diltiazem)

Contraindications / Cautions

Known hypersensitivity to amlodipine
Severe hepatic impairment - dose reduction required
Unstable angina / acute MI (short-acting DHPs are avoided; amlodipine's long t½ poses less concern but caution is warranted)
Cardiogenic shock
Short-acting DHPs (e.g., immediate-release nifedipine) are contraindicated in CAD due to evidence of increased mortality - this concern does not apply to amlodipine given its gradual onset and long action

Comparison with Other CCB Classes

Feature	Amlodipine (DHP)	Verapamil (PAV)	Diltiazem (BTZ)
Vascular selectivity	High	Low	Intermediate
Negative inotropy	Minimal	High	Moderate
Heart rate effect	Mild reflex ↑	↓↓	↓
AV conduction	No effect	Slows	Slows
Use in HFrEF	Safe	Avoid	Avoid
Drug interactions	Moderate	High	Moderate

Overdose

In significant overdose, DHP selectivity is lost - amlodipine can affect all calcium channel types, causing:

Severe hypotension
Cardiogenic shock
Noncardiogenic pulmonary edema (occurs in ~50% of severe poisonings)

Management includes high-dose insulin therapy, calcium gluconate/chloride, vasopressors, and lipid emulsion therapy in refractory cases.

Sources: Goodman & Gilman's Pharmacological Basis of Therapeutics; Lippincott Illustrated Reviews: Pharmacology; Brenner and Rector's The Kidney (2-Volume Set); Harriet Lane Handbook (23rd ed.); Goodman & Gilman's, p. 633-990

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