Calcium channel blockers for Hypertension Treatment: Mechanism and Types- Pharmocology Notes

Calcium channel blockers (CCBs), also known as calcium antagonists, are a class of medications commonly used to treat hypertension (high blood pressure). They work by affecting calcium channels in the heart and blood vessel walls, leading to several physiological changes that help lower blood pressure. Here's how calcium channel blockers work to treat hypertension:

Blocking Calcium Entry: Calcium plays a crucial role in muscle contraction, including the contraction of smooth muscle cells in blood vessel walls and the heart. Calcium channel blockers block the entry of calcium ions into these cells by binding to specific calcium channels in the cell membrane. This action prevents calcium from entering the cells, leading to relaxation of the smooth muscles in blood vessels.

Vasodilation: By blocking calcium channels in the smooth muscle cells of arterial walls, calcium channel blockers induce vasodilation. Vasodilation refers to the widening of blood vessels. When blood vessels relax and dilate, there is less resistance to blood flow, allowing blood to move more freely through the vessels. As a result, peripheral vascular resistance decreases, which leads to a reduction in blood pressure.

Reduced Cardiac Contractility: In addition to affecting blood vessels, some calcium channel blockers, particularly non-dihydropyridine CCBs, also affect the heart. They inhibit calcium entry into cardiac muscle cells, leading to decreased contractility (the force with which the heart muscle contracts). This results in a decrease in the force of each heartbeat and a reduction in cardiac output.

Lower Heart Rate: Some calcium channel blockers, particularly non-dihydropyridine CCBs like verapamil and diltiazem, can also slow down the heart rate by affecting the electrical conduction system of the heart. This reduction in heart rate further decreases cardiac output, contributing to lower blood pressure.

There are two main classes of calcium channel blockers:

Dihydropyridine Calcium Channel Blockers: These drugs primarily affect the smooth muscle cells in blood vessel walls. They are more selective for peripheral vasodilation and are often used to treat hypertension. Examples include amlodipine, nifedipine, and felodipine.

Non-Dihydropyridine Calcium Channel Blockers: These drugs affect both the heart and blood vessels. They are used for various cardiovascular conditions, including hypertension. Examples include verapamil and diltiazem.

List of CCBs prescribed to manage high blood pressure

Amlodipine (Norvasc): Amlodipine is a dihydropyridine calcium channel blocker that primarily affects peripheral blood vessels. It is one of the most widely prescribed CCBs for hypertension. Amlodipine can be used as a standalone medication or in combination with other antihypertensive drugs.

Nifedipine (Procardia, Adalat): Nifedipine is another dihydropyridine CCB used to treat high blood pressure. It is available in immediate-release and extended-release formulations. The extended-release version is preferred for hypertension management to avoid rapid blood pressure fluctuations associated with the immediate-release form.

Felodipine (Plendil): Felodipine is a dihydropyridine CCB used to lower blood pressure. It is typically taken once daily and provides sustained blood pressure control.

Nicardipine (Cardene): Nicardipine is a dihydropyridine CCB that can be used to treat hypertension, especially in certain clinical settings like acute hypertensive emergencies.

Isradipine (DynaCirc): Isradipine is a dihydropyridine CCB indicated for the management of hypertension.

Verapamil (Calan, Isoptin): Verapamil is a non-dihydropyridine CCB that affects both the heart and blood vessels. It is used to treat hypertension as well as certain heart rhythm disorders (arrhythmias) and angina.

Diltiazem (Cardizem, Tiazac): Diltiazem is another non-dihydropyridine CCB that can be prescribed for hypertension, angina, and certain heart rhythm disturbances.