Calcium channel blocking drugs

Which one of the following statements regarding calcium channel blocking drugs is

TRUE?

a) Most of these drugs act on the T-type calcium channel

b) Nifedipine acts mainly by negative inotropy

c) Nimodipine is a class III calcium channel blocking drug

d) Verapamil is a suitable treatment for supraventricular tachycardia

e) Heart block caused by calcium channel blocking drug overdose is treated with

atropine

Answer: d

Explanation

Calcium ion flux is fundamental to excitable tissues. In the cardiovascular system,

myocardial contractility, autorhythmicity and vessel tone may all be reduced by blocking

calcium channels. They are classified according to their predominant effects. Class

I: negative inotropy and chronotropy – useful for hypertension, angina and supraventricular

tachycardia (e.g. verapamil). Class II: reduction in vessel tone with minimal

direct cardiac effect except reflex tachycardia (e.g. nifedipine, nimodipine, nicardipine).

Class III: negative inotropic effects (e.g. diltiazem). They mostly act on L-type

channels and in overdose heart block is usually resistant to atropine. Overdose would

be treated with intravenous calcium chloride, glucagon and catecholamines.

Reference

Yentis S, Hirsch N, Smith G. Anaesthesia and Intensive Care A to Z: An Encyclopaedia of

Principles and Practice, 3rd edn. London: Elsevier, 2004; p.84.