Dihydropyridines act on vessels, non-dihydropyridines on the heart
Expansion
Two classes, distinguished by where they act
- Dihydropyridines (-dipines: amlodipine, nifedipine, felodipine) act on vascular smooth muscle. Vasodilators, used for hypertension and angina. Cause ankle oedema, flushing, headache and reflex tachycardia
- Non-dihydropyridines: verapamil and diltiazem act on the heart, being negatively inotropic and chronotropic. Used for rate control and angina. Cause bradycardia, heart block, and constipation (verapamil particularly)
“The -dipines dilate; verapamil and diltiazem slow.”
The dangerous combination: verapamil with a beta blocker can cause profound bradycardia, complete heart block and asystole, because both suppress the atrioventricular node and contractility. Diltiazem carries the same risk to a lesser degree.
Avoid non-dihydropyridines in heart failure with reduced ejection fraction, since their negative inotropy worsens it. Amlodipine is the safest choice if a calcium channel blocker is needed there.
Ankle oedema from dihydropyridines is caused by precapillary dilatation raising capillary pressure, so it does not respond to diuretics; reduce the dose or add an ACE inhibitor, which dilates the venous side.