Class 4 (Anti-Arrythmics)

Question 1

General MOA of Class 4?

Answer 1

These are L-type Ca channel blockers, in the SA and AV node. It decreases phase 0 (depol) and phase 4 (pacemaker current) of nodal AP, increasing APD and ERP.

Question 2

Among the many Ca channel blockers, which are the special ones used for anti-arrythmics and why?

Answer 2

Verapamil and Diltiazem are the only 2 FDA approved Ca blockers for arrythmias, reason being they have good tropism for cardiac tissue and not blood vessels. If blood vessel Ca channels were blocked we would have hypotension and trigger a reflexive tachycardia, which is pro-arrythmic.

Question 3

Uses for Ca channel blockers (verapamil and Diltiazem)?

Answer 3

Supraventricular tachycardia.

Question 4

Sideeffects of Verapamil and Diltiazem?

Answer 4

Constipation (esp Verapamil), AV block, dizziness, hypotension and flushing.

Question 5

DDI’s to watch out for Ca blockers?

Answer 5

Other drugs that produce AV blocks, ß blockers and digoxin (verapimil displaces digoxin from its binding site, in addition to incurring AV block via digoxin AE).