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Beta Blockers (beta antagonists)


 

Beta blockers, also known as beta antagonists, are drugs that bind to beta-1, and sometimes the beta-2 receptors, causing a conformational change which inhibits the receptor's activity. Beta receptors are found in the lungs, in the uterus, on blood vessels and on cardiac tissue. Normally, epinephrine and norepinephrine stimulate these receptors leading to vasodilation, increased heart rate and contractility, bronchodilation, and relaxation of the muscles of the uterus. Beta blockers that target only the beta-1 receptors(selective B1 antagonists) target mostly the heart, resulting in a decrease in contractility and heart rate. Non selective beta antagonists are more likely to effect the heart, blood vessels and lungs. Beta blockers can cause slight vasoconstriction, this effect is usually not very pronounced because the beta receptors play only a small role in regulating vascular tone, and this effect is more likely to be seen in non selective beta blockers. At very high concentrations, selective beta-1 antagonists begin to also effect the beta-2 receptors, acting in a non selective way.

Beta blockers are used to treat heart arrhythmias, high blood pressure, anxiety, shaking as a result of antipsychotic use, chest pain(angina), heart failure, glaucoma, migraines, heart attacks, pheochromocytoma and other acute conditions.

Some beta blockers are able to cross the blood brain barrier, allowing them to enter the CNS. The lipophilicity of the drug tends to render it able to cross into the CNS (propranolol, metoprolol, pindolol). This is why some beta blockers can be helpful in treating anxiety.

Carvedilol and Labetolol are unique because they are also able to antagonize the alpha-1 receptors. Stimulation of the alpha receptors cause vasoconstriction, and therefore blocking these receptors can decrease blood pressure. Carvedilol and Labetolol have a much greater affinity for the beta receptors, but still have low-moderate ability to block the alpha receptors. Carvedilol is unique in that it has antioxidant effects, making it extra useful in the treatment of heart failure by protecting the heart against oxidative damage.

Esmolol is unique because it contains an ester functional group, making it susceptible to metabolism from esterase enzymes. This is significant because it gives the drug a very short half life of about 8 minutes, making it useful in surgical procedures.



Selective Beta Blockers:

Acebutolol

Atenolol

Betaxolol

Esmolol

Metoprolol

Bisoprolol

Nebivolol



Non Selective Beta Blockers:

Bunolol

Carteolol

Metipranolol

Nadolol

Penbutolol

Pindolol

Sotalol

Propranolol

Timolol





Alpha and Beta blocking activity:

Labetalol

Carvedilol









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