Study notes on Calcium Channel Blockers (CCBs):1. Classification

• Non-dihydropyridines:

  • Verapamil → primarily cardiac effects

  • Diltiazem → cardiac + some vascular effects

• Dihydropyridines (DHPs):

  • Amlodipine, Nifedipine, Nicardipine, Nimodipine (all end in -dipine)

  • Primarily act on vascular smooth muscle

2. Mechanism of Action

• Non-DHPs:

  • Inhibit SA node → ↓ heart rate

  • Inhibit AV node → ↓ conduction (good for arrhythmias)

  • Inhibit L-type Ca²⁺ channels in myocardium → ↓ contractility

• DHPs:

  • Inhibit L-type Ca²⁺ channels in vascular smooth muscle (tunica media)

  • → Vasodilation → ↓ TPR → ↓ blood pressure & afterload

• Cellular Effects:

  • Blocking L-type Ca²⁺ channels → ↓ Ca²⁺ influx

  • In cardiac cells → ↓ depolarization, ↓ cross-bridge cycling → ↓ contractility

  • In vascular smooth muscle → ↓ calmodulin activation → ↓ MLCK phosphorylation → vasodilation

3. Indications

• Arrhythmias (non-DHPs: verapamil, diltiazem)

  • Atrial fibrillation (rate control)

  • Atrial flutter

  • Supraventricular tachycardia (SVT)

  • Symptomatic premature atrial contractions (PACs)

• Angina

  • Stable angina (if beta-blockers not tolerated)

  • Prinzmetal’s (vasospastic) angina (DHPs useful)

• Hypertension

  • Chronic hypertension

  • Hypertensive emergency (nicardipine, nifedipine)

  • Safe in pregnancy (nifedipine)

• Other Uses

  • Raynaud’s phenomenon (vasodilation)

  • Subarachnoid hemorrhage vasospasm (nimodipine)

  • Cluster headache prophylaxis

  • Achalasia (relax LES, less effective but possible adjunct)

4. Side Effects

• Cardiac effects (non-DHPs):

  • Bradycardia

  • AV block

  • Hypotension

  • Worsening of heart failure (↓ contractility)

• Vascular effects (DHPs):

  • Reflex tachycardia

  • Hypotension, orthostatic hypotension

  • Flushing (cutaneous vasodilation)

  • Peripheral edema (capillary leakage)

• GI effects:

  • Constipation (esp. verapamil)

• Dental:

  • Gingival hyperplasia (esp. amlodipine)

• Endocrine (verapamil):

  • Hyperprolactinemia →

    • Men: gynecomastia

    • Women: galactorrhea, menstrual irregularities

5. Contraindications

• Do NOT use in:

  • Wolff-Parkinson-White syndrome with AFib (risk of VT/VF)

  • Concomitant beta-blocker therapy (risk of severe bradycardia/heart block)

  • Heart block (2nd or 3rd degree)

  • Severe hypotension

  • Decompensated heart failure

  • Severe aortic stenosis

6. Antidote for Toxicity

• High-dose calcium (calcium gluconate or calcium chloride) → outcompetes the blocker at L-type Ca²⁺ channels

Key memory hooks:

• Non-DHPs = Node (SA/AV node) + Negative inotropy

• DHPs = Dilation (vasodilation, afterload reduction)

• Watch for gingival hyperplasia (amlodipine) and constipation (verapamil).