It has 1000X greater affinity for alpha 1 vs alpha 2 receptors. It is a short acting drug with a duration of action of about 4 to 6 hours. Terazosin is a close structural analogue of prazosin with similar pharmacological effects, but an intermediate duration of action, ie approximately 18 hours. Doxazosin is another structural analogue with similar pharmacological effects to prazosin, but with a long duration of action, ie 36 hours. That is marked postural hypotension and fainting 30-90 minutes after the first dose, or with the addition of a second antihypertensive drug to a patient already taking one of these agents.
Postural hypotension is another side effect.
A major use of these drugs is in the treatment of hypertension. I. Miscellaneous drugs with alpha adrenergic blocking activity 1. The ergot alkaloids were the first adrenergic blocking agents to be discovered. Ergot is a fungus which grows on rye which contains many biologically active components. Ergotism is a disease characterized by profound vasoconstriction , ischemia, and gangrene of the affected limb.