Pharmacology of major drug classes used - calcium channel blockers

Mechanism

Block L-type calcium channels, reducing calcium influx into vascular smooth muscle and cardiac myocytes - divided into two pharmacologically distinct subclasses with different clinical uses

Subclass	Example	Selectivity	Main use
Dihydropyridines	Amlodipine, felodipine	Vascular smooth muscle >> cardiac	Hypertension, angina - minimal negative chronotropic/inotropic effect
Non-dihydropyridines	Verapamil, diltiazem	Cardiac (AV node, myocardium) > vascular	Rate control (AF/SVT), angina - negative chronotropic/inotropic

Never combine a non-dihydropyridine CCB with a beta-blocker - both suppress AV nodal conduction and contractility - risk of severe bradycardia/heart block/cardiogenic shock
Verapamil/diltiazem are contraindicated in decompensated heart failure with reduced EF (negative inotropy); dihydropyridines are relatively safe in HFrEF if a CCB is needed for another indication (e.g. amlodipine for resistant hypertension)
Side effects: dihydropyridines - peripheral oedema (precapillary vasodilation, not fluid overload - does not respond well to diuretics), flushing, headache; non-dihydropyridines - constipation (verapamil), bradycardia

Hypertension, stable angina, rate control in AF/SVT (non-DHP), CCB/beta-blocker overdose

Peripheral oedema from dihydropyridines is often mistaken for fluid overload and treated with diuretics inappropriately - recognising the mechanism (vasodilation, not volume) avoids unnecessary treatment

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