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Classification of Calcium Channel Blockers (CCBs)
1. Dihydropyridines
- Examples: Amlodipine, Nifedipine, Felodipine, Isradipine, Nicardipine.
- Mechanism: Primarily act on vascular smooth muscle, causing vasodilation and reduced peripheral vascular resistance.
2. Non-Dihydropyridines
- Examples: Verapamil, Diltiazem.
- Mechanism: Affect both vascular smooth muscle and cardiac muscle, decreasing heart rate and myocardial contractility.
Mechanism of Action
Calcium channel blockers inhibit the influx of calcium ions through L-type calcium channels, leading to:
- Vasodilation of peripheral arteries and decreased blood pressure.
- Decreased myocardial contractility (especially with non-dihydropyridines).
- Slowed conduction through the AV node (particularly non-dihydropyridines).
Therapeutic Doses
- Amlodipine: 2.5 to 10 mg once daily.
- Nifedipine: 30 to 90 mg per day (extended-release).
- Verapamil: 80 to 480 mg per day (depending on formulation).
- Diltiazem: 120 to 540 mg per day (depending on formulation).
Indications
- Hypertension
- Angina pectoris
- Supraventricular tachycardia
- Atrial fibrillation
- Raynaud's phenomenon
- Migraines
Adverse Effects
Dihydropyridines:
- Peripheral edema
- Flushing
- Headache
- Reflex tachycardia
Non-Dihydropyridines:
- Bradycardia
- Heart block
- Constipation (more common with verapamil)
- Dizziness and fatigue
Contraindications
- Severe hypotension
- Heart block (especially without a pacemaker)
- Severe heart failure
- Known hypersensitivity
- Concurrent use with beta-blockers (particularly non-dihydropyridines)
