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Some beta blockers (e.g. oxprenolol, pindolol, penbutolol, labetalol and acebutolol) exhibit intrinsic sympathomimetic activity (ISA). These agents are capable of exerting low-level agonist activity at the β-adrenergic receptor while simultaneously acting as a receptor site antagonist .
Acebutolol is a cardioselective beta-1 blocker which also considered a partial agonist due to its intrinsic sympathomimetic activity (ISA). This means it provides low-grade beta stimulation at rest but acting as typical beta-blockers when sympathetic activity is high. [3]
The mechanisms of sympathomimetic drugs can be direct-acting (direct interaction between drug and receptor), such as α-adrenergic agonists, β-adrenergic agonists, and dopaminergic agonists; or indirect-acting (interaction not between drug and receptor), such as MAOIs, COMT inhibitors, release stimulants, and reuptake inhibitors that increase the levels of endogenous catecholamines.
Figure 1: The chemical structure of dichloroisoprenaline or dichloroisoproterenol (), abbreviated DCI — the first β-blocker to be developed. β adrenergic receptor antagonists (also called beta-blockers or β-blockers) were initially developed in the 1960s, for the treatment of angina pectoris but are now also used for hypertension, congestive heart failure and certain arrhythmias. [1]
Beta-blockers with intrinsic sympathomimetic activity: acebutolol, pindolol; Some common side effects include increased airway resistance for non-selective beta-blockers, exacerbation of peripheral vascular diseases, and hypotension [15] Beta-blockers are contraindicated in patients with second- or third-degree atrioventricular block.
Beta blockers work by blocking the effects of adrenaline, aka slowing your heart rate and reducing those physical signs and symptoms of nervousness and anxiety, he explained.
Doxazosin (alpha blocker) Beta blockers Non-selective agents Alprenolol; Bucindolol; Carteolol; Carvedilol (has additional α-blocking activity) Labetalol (has additional α-blocking activity) Nadolol; Penbutolol (has intrinsic sympathomimetic activity) Pindolol (has intrinsic sympathomimetic activity) Propranolol; Sotalol; Timolol; β 1 ...
Labetalol has intrinsic sympathomimetic activity. [17] It is also an antagonist of the α 1 -adrenergic receptor , and hence is additionally an alpha blocker . The antagonism of the adrenergic receptors by labetalol is competitive against other catecholamines [ 18 ] and its actions on the receptors are potent and reversible . [ 16 ]