Only drugs which block L type of channels, which are large in conductance are effective.
Nifedipine has different binding sites –lower dose is required. It only affects blood vessels and not heart.
Verapamil has maximum effect on heart, while less on blood vessels.
Diltiazem has effects which the in between the other two.
Ca++ channel blockers produce effects mainly on the arterial side. Postural hypotension does not occur.
Mechanism of action and Uses:
- Decrease TPR, blood pressure and systolic wall stress which is beneficial in angina pectoris.
- Effect SA node
a. Verapamil and diltiazem decrease rate causing bradycardia
b. Nifedipine does not, might produce reflex tachycardia
c. In vasospastic angina used because dilate vessels
d. Supraventricular tachycardia –used because block conduction through AV node.
But as side effect, may produce bradycardia and heart blocks.
- Salt and water retention
In ischemic heart disease Ca++ channel blockers may be combined even with beta blockers, but one needs to be very cautious, because both cause decrease in AV conduction and bradycardia.
Sometimes nifedipine is combined with beta blockers. Nitrates and nifedipine produce reflex tachycardia, if they are combined with beta blockers, no reflex tachycardia is seen.