Prazosin

Prazosin
Adult Indications & Dosage
Pediatric Indications & Dosage
Contraindications
Warnings & Precautions
Adverse Reactions
Drug Interactions
Use in Specific Populations
Administration & Monitoring
Overdosage
Pharmacology
Clinical Studies
How Supplied
Images
Patient Counseling Information
Precautions with Alcohol
Brand Names
Look-Alike Names

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: João André Alves Silva, M.D. [2]

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Overview

Prazosin is a alpha-adrenergic blocker that is FDA approved for the {{{indicationType}}} of treatment of hypertension. Common adverse reactions include orthostatic hypotension, palpitations, nausea, asthenia, dizziness, headache, lethargy and somnolence.

Adult Indications and Dosage

FDA-Labeled Indications and Dosage (Adult)

Hypertension

• Initial dose:

• 1 mg two or three times a day

• Maintenance dose:

• Dosage may be slowly increased to a total daily dose of 20 mg given in divided doses. The therapeutic dosages most commonly employed have ranged from 6 mg to 15 mg daily 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.

• Use with other drugs:

• When adding a diuretic or other antihypertensive agent, the dose of prazosin should be reduced to 1 mg or 2 mg three times a day and retitration then carried out.
• Concomitant administration of prazosin with a PDE-5 inhibitor can result in additive blood pressure lowering effects and symptomatic hypotension; therefore, PDE-5 inhibitor therapy should be initiated at the lowest dose in patients taking prazosin.

Off-Label Use and Dosage (Adult)

Guideline-Supported Use

Benign prostatic hyperplasia

• Class of Recommendation: Class IIb

• Strength of Evidence: Category B

• Dosing Information/Recommendation

• (Dosage)

Dream disorder - posttraumatic stress disorder

• Class of Recommendation: Class IIb

• Strength of Evidence: Category B

• A 6-week open-label trial, with 5 patients, with history of exposure to civilian trauma, in a non-military environment, who subsequently developed posttraumatic stress disorder (PTSD):

• 1 to 4 mg/day

• An 8-week open-label trial, with 4 patients, with history of combat trauma nightmares and chronic DSM-IV posttraumatic stress disorder (PTSD) with concomitant severe intractable combat trauma nightmares:

• 2 to 10 mg/day

Erectile dysfunction

• Class of Recommendation: Class IIb

• Strength of Evidence: Category B

• Dosing Information/Recommendation

• (Dosage)

Poisoning due to scorpion venom

• Class of Recommendation: Class IIb

• Strength of Evidence: Category B

• Dosing Information/Recommendation

• (Dosage)

Raynaud's phenomenon

• Class of Recommendation: Class IIb

• Strength of Evidence: Category B

• Dosing Information/Recommendation

• (Dosage)

Non–Guideline-Supported Use

Condition 1

• Dosing Information

• (Dosage)

Condition 2

• Dosing Information

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Condition 3

• Dosing Information

• (Dosage)

Pediatric Indications and Dosage

FDA-Labeled Indications and Dosage (Pediatric)

Condition 1

• Dosing Information

• (Dosage)

Condition 2

• Dosing Information

• (Dosage)

Off-Label Use and Dosage (Pediatric)

Guideline-Supported Use

Condition 1

• Developed by: (Organisation)

• Class of Recommendation: (Class) (Link)

• Strength of Evidence: (Category A/B/C) (Link)

• Dosing Information/Recommendation

• (Dosage)

Condition 2

• Developed by: (Organisation)

• Class of Recommendation: (Class) (Link)

• Strength of Evidence: (Category A/B/C) (Link)

• Dosing Information/Recommendation

• (Dosage)

Non–Guideline-Supported Use

Condition 1

• Dosing Information

• (Dosage)

Condition 2

• Dosing Information

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Condition 3

• Dosing Information

• (Dosage)

Contraindications

• Prazosin is contraindicated in patients with known sensitivity to:

• Quinazolines
• Prazosin
• Any of the inert ingredients

Warnings

• Prazosin, as other alpha-blockers, may cause:

• Syncope with sudden loss of consciousness:

• May be 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 per minute
• Syncopal episodes have usually occurred within 30 to 90 minutes of the initial dose of the drug
• These have often been reported in association with rapid dosage increases or the introduction of another antihypertensive drug into the regimen of a patient taking high doses of prazosin.
• The incidence of syncopal episodes is approximately 1% in patients given an initial dose of 2 mg or greater.
• Clinical trials conducted during the investigational phase of this drug suggest that syncopal episodes can be minimized by limiting the initial dose of the drug to 1 mg, by subsequently increasing the dosage slowly, and by introducing any additional antihypertensive drugs into the patient's regimen with caution.
• If syncope occurs, the patient should be placed in the recumbent position and treated supportively as necessary. This adverse effect is self-limiting and in most cases does not recur after the initial period of therapy or during subsequent dose titration.

• Hypotension may develop in patients given prazosin who are also receiving a beta-blocker such as propranolol.
• Patients should always be started on the 1 mg capsules of prazosin. The 2 and 5 mg capsules are not indicated for initial therapy.
• More common than loss of consciousness are the symptoms often associated with lowering of the blood pressure, namely:

• Dizziness
• Lightheadedness.

• The patient should be cautioned about these possible adverse effects and advised what measures to take should they develop. The patient should also be cautioned to avoid situations where injury could result should syncope occur during the initiation of prazosin therapy.

Adverse Reactions

Clinical Trials Experience

• Clinical trials were conducted on more than 900 patients. During these trials and subsequent marketing experience, the most frequent reactions associated with prazosin therapy are:

• Dizziness 10.3%
• Headache 7.8%
• Drowsiness 7.6%
• Lack of energy 6.9%
• Weakness
• Palpitations 5.3%
• Nausea 4.9%.

• In most instances, side effects have disappeared with continued therapy or have been tolerated with no decrease in dose of drug.
• Less frequent adverse reactions which are reported to occur in 1–4% of patients are:

Central Nervous System

• Vertigo
• Depression
• Nervousness

Cardiovascular

• Edema
• Orthostatic hypotension
• Dyspnea
• Syncope

Gastrointestinal

• Vomiting
• Diarrhea
• Constipation

Miscellaneous

• Rash
• Urinary frequency
• Blurred vision
• Reddened sclera
• Epistaxis
• Dry mouth
• Nasal congestion

• Fewer than 1% of patients have reported the following:

Gastrointestinal

• Abdominal discomfort
• Liver function abnormalities
• Pancreatitis

Cardiovascular

• Tachycardia

Central Nervous System

• Paresthesia
• Hallucinations

Dermatologic

• Pruritus
• Alopecia
• Lichen planus

Genitourinary

• Incontinence
• Impotence
• Priapism

EENT

• Tinnitus

Miscellaneous

• Diaphoresis
• Fever
• Positive ANA titer
• Arthralgia

• Single reports of pigmentary mottling and serous retinopathy, and a few reports of cataract development or disappearance have been reported. In these instances, the exact causal relationship has not been established because the baseline observations were frequently inadequate.

• In more specific slit-lamp and funduscopic studies, which included adequate baseline examinations, no drug-related abnormal ophthalmological findings have been reported.

• Literature reports exist associating prazosin therapy with a worsening of pre-existing narcolepsy. A causal relationship is uncertain in these cases.

Postmarketing Experience

General

• Allergic reaction
• Asthenia
• Malaise
• Pain

Autonomic Nervous System

• Flushing

Cardiovascular

• Angina pectoris
• Hypotension
• Bradycardia

Endocrine

• Gynecomastia

Psychiatric

• Insomnia

Skin/Appendages

• Urticaria

Vascular

• Vasculitis

Vision

• Eye pain

Special Senses

• During cataract surgery, a variant of small pupil syndrome known as Intraoperative Floppy Iris Syndrome (IFIS) has been reported in association with alpha-1 blocker therapy

Drug Interactions

• Prazosin has been administered without any adverse drug interaction in limited clinical experience to date with the following:

• Cardiac glycosides:

• Digitalis
• Digoxin

• Hypoglycemics:

• Insulin
• Chlorpropamide
• Phenformin
• Tolazamide
• Tolbutamide

• Tranquilizers and sedatives:

• Chlordiazepoxide
• Diazepam
• Phenobarbital

• Antigout

• Allopurinol
• Colchicine
• Probenecid

• Antiarrhythmics

• Procainamide
• Propranolol
• Quinidine

• Analgesics, antipyretics and anti-inflammatories

• Propoxyphene
• Aspirin
• Indomethacin
• Phenylbutazone

• Addition of a diuretic or other antihypertensive agent to prazosin has been shown to cause an additive hypotensive effect. This effect can be minimized by reducing the prazosin dose to 1 to 2 mg three times a day, by introducing additional antihypertensive drugs cautiously, and then by retitrating prazosin based on clinical response.

• Concomitant administration of prazosin with a phosphodiesterase-5 inhibitor can result in:

• Additive blood pressure lowering effects
• Symptomatic hypotension

Use in Specific Populations

Pregnancy

Pregnancy Category (FDA): C

• Prazosin has been shown to be associated with decreased litter size at birth, 1, 4, and 21 days of age in rats when given doses more than 225 times the usual maximum recommended human dose.

• No evidence of drug-related external, visceral, or skeletal fetal abnormalities were observed.

• No drug-related external, visceral, or skeletal abnormalities were observed in fetuses of pregnant rabbits and pregnant monkeys at doses more than 225 times and 12 times the usual maximum recommended human dose, respectively.

• The use of prazosin and a beta-blocker for the control of severe hypertension in 44 pregnant women revealed no drug-related fetal abnormalities or adverse effects.

• Therapy with prazosin was continued for as long as 14 weeks.

• Prazosin has also been used alone or in combination with other hypotensive agents in severe hypertension of pregnancy by other investigators. No fetal or neonatal abnormalities have been reported with the use of prazosin.

• There are no adequate and well controlled studies which establish the safety of prazosin in pregnant women. Prazosin should be used during pregnancy only if the potential benefit justifies the potential risk to the mother and fetus.

Pregnancy Category (AUS): (Description)

Labor and Delivery

(Description)

Nursing Mothers

(Description)

Pediatric Use

(Description)

Geriatic Use

(Description)

Gender

(Description)

Race

(Description)

Renal Impairment

(Description)

Hepatic Impairment

(Description)

Females of Reproductive Potential and Males

(Description)

Immunocompromised Patients

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Others

(Description)

Administration and Monitoring

Administration

(Oral/Intravenous/etc)

Monitoring

Condition 1

(Description regarding monitoring, from Warnings section)

Condition 2

(Description regarding monitoring, from Warnings section)

Condition 3

(Description regarding monitoring, from Warnings section)

IV Compatibility

Solution

Compatible

• Solution 1
• Solution 2
• Solution 3

Not Tested

• Solution 1
• Solution 2
• Solution 3

Variable

• Solution 1
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Incompatible

• Solution 1
• Solution 2
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Y-Site

Compatible

• Solution 1
• Solution 2
• Solution 3

Not Tested

• Solution 1
• Solution 2
• Solution 3

Variable

• Solution 1
• Solution 2
• Solution 3

Incompatible

• Solution 1
• Solution 2
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Admixture

Compatible

• Solution 1
• Solution 2
• Solution 3

Not Tested

• Solution 1
• Solution 2
• Solution 3

Variable

• Solution 1
• Solution 2
• Solution 3

Incompatible

• Solution 1
• Solution 2
• Solution 3

Syringe

Compatible

• Solution 1
• Solution 2
• Solution 3

Not Tested

• Solution 1
• Solution 2
• Solution 3

Variable

• Solution 1
• Solution 2
• Solution 3

Incompatible

• Solution 1
• Solution 2
• Solution 3

TPN/TNA

Compatible

• Solution 1
• Solution 2
• Solution 3

Not Tested

• Solution 1
• Solution 2
• Solution 3

Variable

• Solution 1
• Solution 2
• Solution 3

Incompatible

• Solution 1
• Solution 2
• Solution 3

Overdosage

Acute Overdose

Signs and Symptoms

(Description)

Management

(Description)

Chronic Overdose

Signs and Symptoms

(Description)

Management

(Description)

Pharmacology

Prazosin
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Mechanism of Action

(Description)

Structure

(Description with picture)

Pharmacodynamics

(Description)

Pharmacokinetics

(Description)

Nonclinical Toxicology

(Description)

Clinical Studies

Condition 1

(Description)

Condition 2

(Description)

Condition 3

(Description)

How Supplied

(Description)

Storage

There is limited information regarding Prazosin Storage in the drug label.

Images

Drug Images

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Package and Label Display Panel

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Patient Counseling Information

(Patient Counseling Information)

Precautions with Alcohol

Alcohol-Prazosin interaction has not been established. Talk to your doctor about the effects of taking alcohol with this medication.

Brand Names

There is limited information regarding Prazosin Brand Names in the drug label.

Look-Alike Drug Names

• (Paired Confused Name 1a) — (Paired Confused Name 1b)
• (Paired Confused Name 2a) — (Paired Confused Name 2b)
• (Paired Confused Name 3a) — (Paired Confused Name 3b)

Drug Shortage Status

Drug Shortage

Price

References

The contents of this FDA label are provided by the National Library of Medicine.