Calcium channel blocker
Introduction
Calcium channel blockers (CCBs) are a class of medications that disrupt the movement of calcium (Ca2+) through calcium channels. They are primarily used to manage hypertension and cardiac arrhythmias.
Mechanism of Action
Calcium channel blockers work by blocking voltage-dependent calcium channels (VDCCs) in cardiac muscle and blood vessel walls. This action inhibits the influx of calcium ions into these cells. Calcium ions play a crucial role in the contraction of smooth and cardiac muscle cells. By inhibiting the influx of calcium ions, CCBs cause a decrease in contractile activity, leading to a reduction in blood pressure and heart rate.
Classification
Calcium channel blockers are classified into two major groups based on their chemical structure and vascular selectivity: dihydropyridines and non-dihydropyridines.
Dihydropyridines
Dihydropyridines (DHPs) are a class of CCBs that primarily act on the L-type calcium channels in the smooth muscle cells of the arterial walls. They are potent vasodilators and are primarily used to treat hypertension.
Examples of DHPs include amlodipine, nifedipine, and nicardipine.
Non-dihydropyridines
Non-dihydropyridines include two subclasses: phenylalkylamines and benzothiazepines. They have more of an effect on the heart than on the blood vessels.
Phenylalkylamines, such as verapamil, primarily affect the heart and are used to treat cardiac arrhythmias and angina.
Benzothiazepines, such as diltiazem, have a balanced effect on the heart and blood vessels. They are used to treat both hypertension and angina.
Pharmacokinetics
The pharmacokinetics of calcium channel blockers vary significantly between different drugs and are influenced by factors such as absorption, distribution, metabolism, and excretion.
Adverse Effects
While calcium channel blockers are generally well-tolerated, they may cause some adverse effects. These can include dizziness, flushing, headache, and edema. In rare cases, they can cause serious cardiac adverse effects such as bradycardia or heart block.
Clinical Uses
Calcium channel blockers are used in the management of several cardiovascular conditions, including hypertension, angina, and certain types of cardiac arrhythmias. They are also used off-label for the prevention of migraines and Raynaud's phenomenon.
Contraindications and Precautions
Calcium channel blockers are contraindicated in patients with certain conditions, such as severe hypotension, sick sinus syndrome, and second- or third-degree heart block. They should be used with caution in patients with heart failure, hepatic impairment, or renal impairment.
Interactions
Calcium channel blockers can interact with a number of other medications, including beta blockers, digoxin, and statins. These interactions can lead to changes in the effectiveness of the medications or an increased risk of adverse effects.