Calcium channel blockers are commonly used antihypertensive agents that relax vascular smooth muscle and reduce vascular resistance. They do this by inhibiting the movement and binding of calcium ions, which play an integral role in regulating skeletal and smooth muscle contractility and in the performance of the normal and diseased heart. Two types of calcium channel blockers are used in clinical situations: those that are selective for L-type (long-lasting, large-current, or slow), voltage-dependent calcium channels, and those that are nonselective. In clinical practice, selective agents are primarily used.
Often considered a homogeneous family of drugs, selective calcium channel blockers actually have marked individual differences in chemical structure, binding site, tissue selectivity, and, consequently, clinical activity and therapeutic indications. These agents can be grouped into three discrete chemical classes: the phenylalkylamines (eg, verapamil), the benzothiazepines (eg, diltiazem), and the 1,4-dihydropyridines (eg, nifedipine). Verapamil and diltiazem are pharmacologically more similar to each other than either is to the dihydropyridines, which has prompted some authors to recommend delineating verapamil and diltiazem (nondihydropyridines) as one subgroup of calcium channel blockers and the dihydropyridines as another.1,2