Pharmacology of Beta-adrenergic Blockers

Beta-adrenergic Blockers
Beta-adrenergic blockers (β-blockers) block the beta 1 receptor site. Beta-blockers decrease the eff ects of the sympathetic nervous system by blocking the release of the catecholamines epinephrine and norepinephrine, thereby decreasing the heart rate and blood pressure.

Mechanism of Action
Beta blockers reduce oxygen demand, both at rest and during exertion, in the myocardium, and prevent myocardial infarction (IM).

Indications
Th e beta-blockers reduce the frequency and severity of exertional angina that is not controlled by nitrates. Th erefore, these are an important part of therapy for angina pectoris. Combined therapy with nitrates is oft en preferred in the treatment of angina pectoris, because of a decrease in the side eff ects of both agents.

Adverse Effects
Beta-blockers have few adverse eff ects on the respiratory and cardiovascular systems. Common adverse eff ects of these drugs include dyspnea, bronchospasm, hypotension, bradycardia, and hypoglycemia. These agents may also cause insomnia and depression.

Contraindications and Precautions
β-blockers are contraindicated in patients with a known hypersensitivity to these agents. β-blockers are also contraindicated for use in patients with asthma, congestive heart failure, heart block, bradycardia, and diabetes mellitus. These drugs should be avoided in patients with cardiogenic shock, pulmonary edema, and peripheral vascular disease.β-adrenergic blockers should be used with caution in patients prone to non-allergenic bronchospasm (e.g., chronic bronchitis, emphysema), major surgery, stroke, renal disease, or hepatic disease. β-blockers are used cautiously in elderly patients, patients with diabetes mellitus, and in patients prone to hypoglycemia.

Drug Interactions
These agents may interact with atropine and other anticholinergics, NSAIDs, insulin, sulfonylureas, lidocaine, verapamil, prazosin, and terazosin.