ADRENERGIC ANTAGONISTS

Introduction: Adrenergic antagonists act by directly blocking adrenergic receptors. The actions of these drugs are specific to either alpha or beta blockade. Medications in this class have great therapeutic application and are the most widely prescribed class of autonomic nervous system drugs.

1) Alpha-adrenergic antagonists, or simply alpha blockers, are used for their effects on vascular smooth muscle. By relaxing vascular smooth muscle in small arteries, alpha1 blockers such as doxazosin cause vasodilation, decreasing Blood Pressure. They may be used either alone or in combination with other agents in the treatment of hypertension.

2) A second use is in the treatment of Benign Prostatic Hyperplasia (BPH), due to their ability to increase urine flow by relaxing smooth muscle in the bladder neck, prostate, and urethra.

Side effects: The most common adverse effect of alpha blockers is orthostatic hypotension, which occurs when a patient abruptly changes from a recumbent to an upright position. Reflex tachycardia, nasal congestion, and impotence are other important side effects that may occur as a consequence of increased parasympathetic activity.

Beta-adrenergic antagonists may block beta1 receptors, beta2 receptors, or both types of receptors. Regardless of their receptor specificity, all beta blockers are used therapeutically for their effects on the cardiovascular system. Beta blockers decrease the rate and force of contraction of the heart and slow electrical conduction through the atrioventricular node. Drugs that selectively block beta1 receptors, such as atenolol, are called cardioselective agents. Because they have little effect on noncardiac tissue, they exert fewer side effects than nonselective agents such as propranolol.

3) The primary use of beta blockers is in the treatment of hypertension. Although the exact mechanism by which beta blockers reduce BP is not completely understood, it is thought that the reduction may be due to decreased cardiac output or to suppression of renin release by the kidneys.

4) By decreasing the cardiac workload, beta blockers can ease the pain associated with migraines and angina pectoris.

5) By slowing electrical conduction across the myocardium, beta blockers are useful in treating certain types of dysrhythmias.

6) Other therapeutic uses include the treatment of heart failure, myocardial infarction, and narrow-angle glaucoma.

RELATED;

1.  CHOLINOMIMETICS

2.  PHARMACOLOGY AND THERAPEUTICS

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