| Indication | For treatment of hypertension, symptomatic benign prostatic hyperplasia, and severe congestive heart failure. May also be used alone or in combination with β-blockers in the preoperative management of signs and symptoms of pheochromocytoma. |
| Pharmacodynamics | Prazosin is an alpha-adrenergic blocking agent used to treat hypertension and benign prostatic hyperplasia. Accordingly, Prazosin is a selective inhibitor of the alpha1 subtype of alpha adrenergic receptors. In the human prostate, Prazosin antagonizes phenylephrine (alpha1 agonist)-induced contractions, in vitro, and binds with high affinity to the alpha1c adrenoceptor, which is thought to be the predominant functional type in the prostate. Studies in normal human subjects have shown that Prazosin competitively antagonized the pressor effects of phenylephrine (an alpha1 agonist) and the systolic pressor effect of norepinephrine. The antihypertensive effect of Prazosin results from a decrease in systemic vascular resistance and the parent compound Prazosin is primarily responsible for the antihypertensive activity. |
| Mechanism of action | Prazosin acts by inhibiting the postsynaptic alpha(1)-adrenoceptors on vascular smooth muscle. This inhibits the vasoconstrictor effect of circulating and locally released catecholamines (epinephrine and norepinephrine), resulting in peripheral vasodilation. |
| Absorption | Well-absorbed from gastrointestinal tract; bioavailability is variable (50 to 85%). |
| Volume of distribution | Not Available |
| Protein binding | 97% |
| Metabolism | Primarily hepatic. Several metabolites have been identified in humans and animals (6- O -demethyl, 7- O -demethyl, 2-[1-piperazinyl]-4-amino-6, 7-dimethoxyquinazoline, 2,4-diamino-6,7-dimethoxyquinazoline). |
| Route of elimination | Animal studies indicate that prazosin hydrochloride is extensively metabolized, primarily by demethylation and conjugation, and excreted mainly via bile and feces. Less extensive human studies suggest similar metabolism and excretion in man. |
| Half life | 2-3 hours |
| Clearance | Not Available |
| Toxicity | Not Available |