Terazosin is a selective alpha1-antagonist used for treatment of symptoms of benign prostatic hyperplasia (BPH). It also acts to lower blood pressure, so it is a drug of choice for men with hypertension and prostate enlargement. It works by blocking the action of adrenaline on smooth muscle of the bladder and the blood vessel walls.
For the treatment of symptomatic BPH and mild to moderate hypertension.
Terazosin, classified as a quinazoline, is similar to doxazosin and prazosin. As an α-adrenergic blocking agent, terazosin is used to treat hypertension and BPH. Terazosin produces vasodilation and reduces peripheral resistance but in general has only a slight effect on cardiac output. The antihypertensive effect with chronic dosing is not usually accompanied by reflex tachycardia.
Mechanism of action
In general, α<sub>1</sub>-adrenergic receptors mediate contraction and hypertrophic growth of smooth muscle cells. α<sub>1</sub>-Receptors are 7-transmembrane domain receptors coupled to G proteins, G<sub>q/11</sub>. Three α<sub>1</sub>-receptor subtypes, which share approximately 75% homology in their transmembrane domains, have been identified: α<sub>1A</sub> (chromosome 8), α<sub>1B</sub> (chromosome 5), and α<sub>1D</sub> (chromosome 20). Terazosin is the first α<sub>1</sub>-receptor antagonist to demonstrate selectivity for the α<sub>1A</sub>-receptor. All three receptor subtypes appear to be involved in maintaining vascular tone. The α<sub>1A</sub>-receptor maintains basal vascular tone while the α<sub>1B</sub>-receptor mediates the vasocontrictory effects of exogenous α<sub>1</sub>-agonists. Activation of α<sub>1</sub>-receptors activates G<sub>q</sub>-proteins, which results in intracellular stimulation of phospholipases C, A<sub>2</sub>, and D. This results in mobilization of Ca<sup>2+</sup> from intracellular stores, activation of mitogen-activated kinase and PI<sub>3</sub> kinase pathways and subsequent vasoconstriction. Terozosin produces its pharmacological effects by inhibiting α<sub>1A</sub>-receptor activation. Inhibition of these receptors in the vasculature and prostate results in muscle relaxation, decreased blood pressure and improved urinary outflow in symptomatic benign prostatic hyperplasia.
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