Prazosin Dosage

This dosage information may not include all the information needed to use Prazosin safely and effectively. See additional information for Prazosin.

The information at Drugs.com is not a substitute for medical advice. ALWAYS consult your doctor or pharmacist.

Usual Adult Dose for:

Additional dosage information:

Usual Adult Dose for Congestive Heart Failure

Initial dose: 1 mg orally 2-3 times a day.
Maintenance dose: 6-15 mg daily given in divided doses.

Usual Adult Dose for Hypertension

Initial dose: 1 mg orally 2-3 times a day.
Maintenance dose: 6-15 mg daily given in divided doses.

Usual Adult Dose for Benign Prostatic Hyperplasia

Initial dose: 1 mg orally 2-3 times a day.
Maintenance dose: 6-15 mg daily given in divided doses.

Renal Dose Adjustments

Data not available

Liver Dose Adjustments

Data not available

Dose Adjustments

Dosage may be slowly increased to a total daily dose of 20 mg given in divided doses. Doses higher than 20 mg usually do not increase efficacy, however a few patients may benefit from further increases up to a daily dose of 40 mg given in divided doses. After initial titration some patients can be maintained adequately on a twice daily dosage regimen.

Precautions

Use of alpha-blockers is generally not considered first-line treatment for hypertension except perhaps when associated with dyslipidemia and/or prostatism. However, data have shown that use of one alpha-blocker (doxazosin) in these patients has been associated with an increased relative risk of cardiovascular events (particularly heart failure) compared with the use of thiazide diuretics.

Prazosin may cause syncope with sudden loss of consciousness. In most cases this is believed due to an excessive postural hypotensive effect. Occasionally, the syncopal episode has been preceded by a bout of severe tachycardia with heart rates of 120-160 beats/min. Syncopal episodes have usually occurred within 30 to 90 minutes of the initial dose. Occasionally they have been reported in association with rapid dosage increases or the introduction of another antihypertensive drug into the regimen of a patient.

Patients should be advised that dizziness or drowsiness may occur after the first dose of this medicine. They should avoid driving or performing hazardous tasks for the first 24 hours after taking this medicine or when the dose is increased. Dizziness, lightheadedness or fainting may occur, especially when rising from a lying or sitting position. Getting up slowly may help lessen the problem. These effects may also occur during periods of alcohol consumption, long periods of standing, exercise, or hot weather.

Intraoperative Floppy Iris Syndrome (IFIS) has been observed in some patients undergoing phacoemulsification cataract surgery while being treated with alpha-1 blockers. Most reports were in patients treated with an alpha-1 blocker at the time IFIS occurred, but in some instances the alpha-1 blocker had been stopped prior to surgery. The manufacturer recommends that patients be questioned to determine whether or not they have taken alpha-1 blockers prior to being considered for cataract surgery. If it is determined that the patient has taken an alpha-1 blocker, the patient's ophthalmologist should be prepared for possible modifications to their surgical technique that may be necessary should IFIS be observed during the procedure. The benefit of stopping therapy prior to cataract surgery has not been established.

Safety and effectiveness in children have not been determined.

Dialysis

Prazosin is not dialyzable because it is protein bound.

Other Comments

When adding a diuretic or other antihypertensive agent, the dose of prazosin should be reduced to 1 mg or 2 mg 3 times a day and retitration then carried out.

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