Overview
This lecture reviews calcium channel blockers (CCBs), differentiates between non-dihydropyridine and dihydropyridine classes, covers mechanisms of action, clinical uses, and important side effects.
Calcium Channel Blocker Classes
- CCBs are divided into non-dihydropyridines (diltiazem, verapamil) and dihydropyridines (amlodipine, nifedipine, clevidipine, etc.).
- Non-dihydropyridines are class 4 antiarrhythmic agents (affecting SA and AV nodes) while dihydropyridines mainly affect vascular smooth muscle.
Mechanism of Action
- Non-dihydropyridines block calcium influx in heart nodal cells, reducing heart rate (negative chronotropy), conduction (negative dromotropy), and contractility (negative inotropy).
- Dihydropyridines block calcium entry in vascular smooth muscle, causing vasodilation and reduced afterload, with little direct effect on heart rate.
Clinical Uses
- Non-dihydropyridines: hypertension, chronic stable and vasospastic angina, rate control in atrial fibrillation with rapid ventricular response (except in WPW syndrome).
- Dihydropyridines: hypertension, angina, certain emergencies (e.g., clevidipine for acute BP control), nimodipine for subarachnoid hemorrhage (start within 96 hours, continue for 21 days).
Drug Interactions & Considerations
- Diltiazem and verapamil inhibit CYP3A4 and P-glycoprotein, causing significant drug interactions (e.g., with digoxin, statins).
- Non-dihydropyridines should not be used with beta blockers or in advanced heart block without pacing.
- All CCBs can cause peripheral edema, constipation, gingival hyperplasia, and have potential bleeding risk due to platelet effects.
Side Effects & Warnings
- Non-dihydropyridines: bradycardia, AV block, worsening heart failure, avoid in WPW syndrome.
- Dihydropyridines: possible reflex tachycardia, more pronounced peripheral edema.
- All CCBs: constipation, gingival hyperplasia, lower extremity edema, rare GI bleeding.
Key Terms & Definitions
- Chronotropy — effect on heart rate.
- Dromotropy — effect on conduction velocity through the AV node.
- Inotropy — effect on the force of heart muscle contraction.
- Afterload — resistance the heart must overcome to eject blood.
- Peripheral edema — swelling in the lower limbs due to fluid leakage from blood vessels.
- WPW syndrome — Wolff-Parkinson-White, an abnormal accessory conduction pathway in the heart.
Action Items / Next Steps
- Review indications and contraindications for each CCB class.
- Memorize key drug interactions for diltiazem and verapamil.
- Read more about management of hypertension and arrhythmias as related to CCBs.