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Side effects associated with phentolamine include headache, flushing, and nasal congestion. [23] Benign prostate hyperplasia, a disease in which urinary retention becomes an issue. Alpha-1 blockers can be used, but it can result in side effects such as increased urination and retrograde ejaculation.
Alpha-adrenergic agonists are a class of sympathomimetic agents that selectively stimulates alpha adrenergic receptors. The alpha-adrenergic receptor has two subclasses α 1 and α 2 . Alpha 2 receptors are associated with sympatholytic properties.
Guanfacine, sold under the brand name Tenex (immediate-release) and Intuniv (extended-release) among others, is an oral alpha-2a agonist medication used to treat attention deficit hyperactivity disorder (ADHD) and high blood pressure. [3] [10] Common side effects include sleepiness, constipation, and dry mouth. [10]
However, the serotonin receptor antagonism has side effects such as weight gain and impaired movement. [11] Hence, alpha-2 blockers are not used clinically due to its extensive binding. Similar to the alpha-1 blocker, the alpha-2 family will also present the first-dose effect, but it is generally less pronounced compared with the alpha-1 ...
Clonidine, sold under the brand name Catapres among others, is an α 2A-adrenergic receptor agonist [12] medication used to treat high blood pressure, ADHD, drug withdrawal (e.g., alcohol, opioids, or nicotine), menopausal flushing, diarrhea, spasticity, and certain pain conditions. [13]
Serious side effects may include low blood pressure with standing and depression. [ 6 ] [ 7 ] Prazosin is a non-selective inverse agonist of the α 1 -adrenergic receptors . [ 6 ] It works to decrease blood pressure by dilating blood vessels and helps with an enlarged prostate by relaxing the outflow of the bladder . [ 6 ]
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.
Currently, several relatively selective alpha-1 antagonists are available. As of 2018, prazosin is the only alpha-1 blocker known to act as an inverse agonist at all alpha-1 adrenergic receptor subtypes; [3] [4] whereas tamsulosin and terazosin are both selective antagonists for all alpha-1 subtypes.