Diltiazem is a calcium channel blocker used to treat hypertension and to manage chronic stable angina. It can be found under the names Cardizem, Cartia, Matzim, Taztia, Tiadylt, and Tiazac. Diltiazem is a benzothiazepine derivative with antihypertensive and vasodilating properties. Approved in 1982 by the FDA, it is a member of the non-dihydropyridine calcium channel blockers drug class. It works through various mechanisms of action, but it primarily works by inhibiting the calcium influx into cardiac and vascular smooth muscle during depolarization. Compared to dihydropyridine drugs, such as nifedipine, that preferentially act on vascular smooth muscle and verapamil that directly acts on the heart muscle, diltiazem displays an intermediate specificity to target both the cardiac and vascular smooth muscle. Being a potent vasodilator, diltiazem is used clinically as an antihypertensive, anti-arrhythmic, and as an anti-anginal agent for the management of cardiovascular conditions such as hypertension, chronic stable angina, atrial fibrillation, atrial flutter. Apart from its main FDA-approved indications, diltiazem has also been used for numerous off-label indications, such as anal fissures (in topical formulations), migraine prophylaxis, pulmonary hypertension, and rest-related cramps in the lower extremities. Typically available in extended-release oral and intravenous formulations, diltiazem is marketed under various brand names with Cardizem and Tiazac being the most common ones. Excitation of cardiac muscle involves the activation of a slow calcium inward current that is induced by L-type slow calcium channels, which are voltage-sensitive, ion-selective channels associated with a high activation threshold and slow inactivation profile. L-type calcium channels are the main current responsible for the late phase of the pacemaker potential. Acting as the main Ca2+ source for contraction in smooth and cardiac muscle, activation of L-type calcium channels allows the influx of calcium ions into the muscles upon depolarization and excitation of the channel. It is proposed that this cation influx may also trigger the release of additional calcium ions from intracellular storage sites. Diltiazem is a slow calcium channel blocker that binds to the extracellular site of the alpha-1C subunit of the channel, which is thought to be the S5-6 linker region of the transmembrane domain IV and/or S6 segment of domain III. Diltiazem can get access to this binding site from either the intracellular or extracellular side, but it requires a voltage-induced conformational changes in the membrane. Diltiazem inhibits the influx of extracellular calcium across the myocardial and vascular smooth muscle cell membranes. In isolated human atrial and ventricular myocardium, diltiazem suppressed tension over the range of membrane potentials associated with calcium channel activity but had little effect on the tension-voltage relations at more positive potentials. This effect is thought to be mediated by the voltage-dependent block of the L-type calcium channels and inhibition of calcium ion release from the ER stores, without altering the sodium-calcium coupled transport or calcium sensitivity of myofilaments. Through inhibition of inward calcium current, diltiazem exerts a direct ionotropic and energy sparing effect on the myocardium. Diltiazem fslows atrioventricular nodal conduction, which is due to its ability to impede slow channel function. Reduced intracellular calcium concentrations equate to increased smooth muscle relaxation resulting in arterial vasodilation and therefore, decreased blood pressure. The decrease in intracellular calcium inhibits the contractile processes of the myocardial smooth muscle cells, causing dilation of the coronary and systemic arteries, increased oxygen delivery to the myocardial tissue, decreased total peripheral resistance, decreased systemic blood pressure, and decreased afterload. Through its actions on reducing calcium levels in cardiac and vascular smooth muscles, diltiazem causes a reduction in the contractile processes of the myocardial smooth muscle cells and vasodilation of the coronary and systemic arteries, including epicardial and subendocardial. Some side effects of using diltiazem may include dizziness, flushing, headache, and weakness.

Diltiazem Calcium Channel Vasodilation Pathway References