Beta Blockers Mechanism Of Action [peopranolol, antenolo, bisoprolol, carvedilol]

beta blockers are one of the most important classes of medications that are primarily used to treat cardiovascuar disease.

Beta blockers are indicated and have FDA approval to treat tachycardia, hypertension, myocardial infarction, congestive heart failure, cardiac arrhythmias as well as hyperthyroidism and even migraine prophylaxis.

starting with an overview of beta receptors, they exist in the body in 3 distinct forms, Beta 1, 2 and 3

beta 1 is located primarily in the heart and mediates cardiac activity, Beta 2 however exists throughout the body in many organ systemscontrol various aspects of metabolic activity and induce smooth muscle relaxation. Beta-3 receptors induce the breakdown of fat cells and are less clinically relevant at present.

to understand the mechanism of action of beta blockers, we have to understand how do beta-adrenocetors work, in this figure we can see how the heart has both B1 and B2 receptors, although predominantly B1, these receptors normally bind to adrenaline and noradrenaline released from the nerve ending or the circulating in the blood. beta receptors are coupled with Gs protein, which activates adenylyl cyclase to form cAMP from ATP, increased cAMP activates cAMP dependent protein kinase (PK-A) that phosphorylates L-type calcium channels, which causes increased calcium entry into the cells. the increased calcium entry during action potential leads to increased inotropy or contractility.

now that we understand how the receptor works, it's easy for us to understand the result of blocking the receptor in patients with mycardial infarction witch results in relaxation of the heart muscle.

Beta-blockers classify as either non-selective and beta-1 selective. Non-selective agents bind to both beta-1 and beta-2 receptors and induce antagonizing effects via both receptors. Examples include propranolol, carvedilol, sotalol, and labetalol. Beta-1 receptor-selective blockers like atenolol, bisoprolol, metoprolol, and esmolol only bind to the beta-1 receptors; therefore, they are cardio-selective

Beta receptors are found all over the body and induce a broad range of physiologic effects. The blockade of these receptors with beta-blocker medications can lead to many adverse effects. Bradycardia and hypotension are two adverse effects that may commonly occur. Fatigue, dizziness, nausea, and constipation are also widely reported. Some patients report sexual dysfunction and erectile dysfunction. All beta-blockers, especially in patients with cardiac risk factors, carry a risk of heart block.

it's worth mentioning that beta blockers are contraindicated in asthmatic patients, that's why it's recommended that only beta1 selective beta blockers can be administered to asthmatics.

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