Which of the following calcium channel blockers is/are phenylalkylamines?

• A. I ONLY
• B. II, III
• C. II ONLY
• D. III ONLY

Answer: (D)

Phenylalkylamines are a group of calcium channel blockers that mainly affect the heart by blocking L-type calcium channels, leading to decreased calcium influx in cardiac tissue. This produces a strong effect on the AV node, slowing conduction (negative dromotropy) and lowering heart rate, with a modest decrease in myocardial contractility (negative inotropy). They differ from dihydropyridines, which primarily cause vasodilation with less direct cardiac effect, and from benzothiazepines, which have intermediate activity.

Among the options, the drug in the third position fits this class: it is a phenylalkylamine. The others belong to the other calcium channel blocker classes and do not share the characteristic strong impact on AV nodal conduction that defines phenylalkylamines.