| Indication | For the treatment of symptomatic BPH and mild to moderate hypertension. |
| Pharmacodynamics | 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, α1-adrenergic receptors mediate contraction and hypertrophic growth of smooth muscle cells. α1-Receptors are 7-transmembrane domain receptors coupled to G proteins, Gq/11. Three α1-receptor subtypes, which share approximately 75% homology in their transmembrane domains, have been identified: α1A (chromosome 8), α1B (chromosome 5), and α1D (chromosome 20). Terazosin is the first α1-receptor antagonist to demonstrate selectivity for the α1A-receptor. All three receptor subtypes appear to be involved in maintaining vascular tone. The α1A-receptor maintains basal vascular tone while the α1B-receptor mediates the vasocontrictory effects of exogenous α1-agonists. Activation of α1-receptors activates Gq-proteins, which results in intracellular stimulation of phospholipases C, A2, and D. This results in mobilization of Ca2+ from intracellular stores, activation of mitogen-activated kinase and PI3 kinase pathways and subsequent vasoconstriction. Terozosin produces its pharmacological effects by inhibiting α1A-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. |
| Absorption | Essentially completely absorbed in man (90% bioavailability). |
| Volume of distribution | Not Available |
| Protein binding | 90-94% |
| Metabolism | Hepatic. One of the four metabolites identified (piperazine derivative of terazosin) has antihypertensive activity. |
| Route of elimination | Approximately 10% of an orally administered dose is excreted as parent drug in the urine and approximately 20% is excreted in the feces. |
| Half life | 12 hours |
| Clearance | Not Available |
| Toxicity | LD50=259.3mg/kg (IV in mice) |