Prazosin dosage

Prazosin was the first example of a selective O -blocker. Its main application is hypertension, usually in combination with a -blocker and/or a diuretic. Orthostatic hypotension readily occurs as a result of venous dilatation. The problem may be avoided by a gradual increase of the dosage. The drug has a short duration of action and must be administered 2-3 times daily in order to achieve adequate control of blood pressure. 

Although less of a problem than with phenoxybenza-mine or phentolamine, symptoms of postural hypotension, such as dizziness and light-headedness, are the most commonly reported side effects associated with prazosin therapy. These effects occur most frequently during initial treatment and when the dosage is sharply increased. Postural hypotension seems to be more pronounced during Na+ dehciency, as may occur in patients on a low-salt diet or being treated with diuretics, (3-blockers, or both. 

The doctor is sympathetic cough is sometimes a problem for patients taking captopril she prescribes an alpha-adrenoceptor (a-adrenoceptor) antagonist, prazosin, instead. Sam has problems initially with orthostatic hypotension however, after dosage reduction, prazosin is well tolerated and Sam s BP settles at 143/87 mmHg. 

Prazosin belongs to the tti-adrenergic antagonist group and can also be administered in portal hypertension at an average dosage of 2-4 mg/day. 

The first-dose effect (profound postural hypotension and reflex tachycardia) is a weU-recognized complication of the first dose of prazosin and related agents. This phenomenon is dose-related and can usually be avoided by using a low initial dosage taken at bedtime. During long-term treatment, orthostatic hypotension and dizziness is reported by about 10% of patients. 

An adverse effect of prazosin and its congeners is the first-dose effect marked postural hypotension and syncope may occur 30-90 minutes after the initial dose. The mechanisms responsible for exaggerated hypotensive response and the subsequent development of tolerance to the effect are not clear an action in the CNS to reduce sympathetic outflow may contribute. Risk of the first-dose phenomenon is minimized by limiting the initial dose (e.g., 1 mg at bedtime), by increasing the dosage slowly, and by introducing additional antihypertensive drugs cautiously. Since orthostatic... 

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