Phenoxybenzamine

Phenoxybenzamine
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: Gerald Chi

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Overview

Phenoxybenzamine is a vasodilator and alpha-adrenergic blocker that is FDA approved for the treatment of pheochromocytoma, to control episodes of hypertension and sweating.. Common adverse reactions include hypotension, tachyarrhythmia, nausea, vomiting, xerostomia, dizziness, somnolence, miosis, nasal congestion, and fatigue.

Adult Indications and Dosage

FDA-Labeled Indications and Dosage (Adult)

Pheochromocytoma

• Dosing Information

• The dosage should be adjusted to fit the needs of each patient. Small initial doses should be slowly increased until the desired effect is obtained or the side effects from blockade become troublesome. After each increase, the patient should be observed on that level before instituting another increase. The dosage should be carried to a point where symptomatic relief and/or objective improvement are obtained, but not so high that the side effects from blockade become troublesome.
• Initially, 10 mg of Dibenzyline (phenoxybenzamine hydrochloride) twice a day. Dosage should be increased every other day, usually to 20 to 40 mg 2 or 3 times a day, until an optimal dosage is obtained, as judged by blood pressure control.
• Long-term use of phenoxybenzamine is not recommended.

Off-Label Use and Dosage (Adult)

Guideline-Supported Use

There is limited information regarding Off-Label Guideline-Supported Use of Phenoxybenzamine in adult patients.

Non–Guideline-Supported Use

There is limited information regarding Off-Label Non–Guideline-Supported Use of Phenoxybenzamine in adult patients.

Pediatric Indications and Dosage

FDA-Labeled Indications and Dosage (Pediatric)

• Safety and effectiveness in pediatric patients have not been established.

Off-Label Use and Dosage (Pediatric)

Guideline-Supported Use

There is limited information regarding Off-Label Guideline-Supported Use of Phenoxybenzamine in pediatric patients.

Non–Guideline-Supported Use

There is limited information regarding Off-Label Non–Guideline-Supported Use of Phenoxybenzamine in pediatric patients.

Contraindications

• Conditions where a fall in blood pressure may be undesirable
• Hypersensitivity to the drug or any of its components.

Warnings

• Dibenzyline-induced alpha-adrenergic blockade leaves beta-adrenergic receptors unopposed. Compounds that stimulate both types of receptors may, therefore, produce an exaggerated hypotensive response and tachycardia.

Precautions

• Administer with caution in patients with marked cerebral or coronary arteriosclerosis or renal damage. Adrenergic blocking effect may aggravate symptoms of respiratory infections.

Adverse Reactions

Clinical Trials Experience

There is limited information regarding Clinical Trial Experience of Phenoxybenzamine in the drug label.

Postmarketing Experience

• The following adverse reactions have been observed, but there are insufficient data to support an estimate of their frequency.

Autonomic Nervous System

Postural hypotension, tachycardia, inhibition of ejaculation, nasal congestion, miosis.

Miscellaneous

Gastrointestinal irritation, drowsiness, fatigue.

Drug Interactions

• Dibenzyline (phenoxybenzamine hydrochloride) may interact with compounds that stimulate both alpha- and beta-adrenergic receptors (i.e., epinephrine) to produce an exaggerated hypotensive response and tachycardia.
• Dibenzyline blocks hyperthermia production by levarterenol, and blocks hypothermia production by reserpine.

Use in Specific Populations

Pregnancy

Pregnancy Category (FDA):

• Pregnancy Category C

• Adequate reproductive studies in animals have not been performed with Dibenzyline (phenoxybenzamine hydrochloride). It is also not known whether Dibenzyline can cause fetal harm when administered to a pregnant woman. Dibenzyline should be given to a pregnant woman only if clearly needed.

Pregnancy Category (AUS):

• Australian Drug Evaluation Committee (ADEC) Pregnancy Category

There is no Australian Drug Evaluation Committee (ADEC) guidance on usage of Phenoxybenzamine in women who are pregnant.

Labor and Delivery

There is no FDA guidance on use of Phenoxybenzamine during labor and delivery.

Nursing Mothers

• It is not known whether this drug is excreted in human milk. Because many drugs are excreted in human milk, and because of the potential for serious adverse reactions from phenoxybenzamine hydrochloride, a decision should be made whether to discontinue nursing or to discontinue the drug, taking into account the importance of the drug to the mother.

Pediatric Use

• Safety and effectiveness in pediatric patients have not been established.

Geriatic Use

There is no FDA guidance on the use of Phenoxybenzamine with respect to geriatric patients.

Gender

There is no FDA guidance on the use of Phenoxybenzamine with respect to specific gender populations.

Race

There is no FDA guidance on the use of Phenoxybenzamine with respect to specific racial populations.

Renal Impairment

There is no FDA guidance on the use of Phenoxybenzamine in patients with renal impairment.

Hepatic Impairment

There is no FDA guidance on the use of Phenoxybenzamine in patients with hepatic impairment.

Females of Reproductive Potential and Males

There is no FDA guidance on the use of Phenoxybenzamine in women of reproductive potentials and males.

Immunocompromised Patients

There is no FDA guidance one the use of Phenoxybenzamine in patients who are immunocompromised.

Administration and Monitoring

Administration

• Oral

• Intravenous

Monitoring

There is limited information regarding Monitoring of Phenoxybenzamine in the drug label.

• Description

IV Compatibility

There is limited information regarding IV Compatibility of Phenoxybenzamine in the drug label.

Overdosage

Acute Overdose

Signs and Symptoms

• These are largely the result of blocking of the sympathetic nervous system and of the circulating epinephrine. They may include postural hypotension, resulting in dizziness or fainting; tachycardia, particularly postural; vomiting; lethargy; shock.

• The oral LD50 for phenoxybenzamine hydrochloride is approximately 2000 mg/kg in rats and approximately 500 mg/kg in guinea pigs.

Management

• When symptoms and signs of overdosage exist, discontinue the drug. Treatment of circulatory failure, if present, is a prime consideration. In cases of mild overdosage, recumbent position with legs elevated usually restores cerebral circulation. In the more severe cases, the usual measures to combat shock should be instituted. Usual pressor agents are not effective. Epinephrine is contraindicated because it stimulates both alpha- and beta- receptors; since alpha- receptors are blocked, the net effect of epinephrine administration is vasodilation and a further drop in blood pressure (epinephrine reversal).

• The patient may have to be kept flat for 24 hours or more in the case of overdose, as the effect of the drug is prolonged. Leg bandages and an abdominal binder may shorten the period of disability.

• I.V. Infusion of levarterenol bitartrate may be used to combat severe hypotensive reactions, because it stimulates alpha-receptors primarily. Although Dibenzyline (phenoxybenzamine hydrochloride) is an alpha -adrenergic blocking agent, a sufficient dose of levarterenol bitartrate will overcome this effect.

Chronic Overdose

There is limited information regarding Chronic Overdose of Phenoxybenzamine in the drug label.

Pharmacology

Mechanism of Action

• Dibenzyline (phenoxybenzamine hydrochloride) is a long-acting, adrenergic, alpha-receptor-blocking agent, which can produce and maintain "chemical sympathectomy" by oral administration. It increases blood flow to the skin, mucosa and abdominal viscera, and lowers both supine and erect blood pressures. It has no effect on the parasympathetic system.

Structure

• Each Dibenzyline capsule, with red cap and body, is imprinted WPC 001 and 10 mg, and contains 10 mg of Phenoxybenzamine Hydrochloride USP. Inactive ingredients consist of D&C Red No. 33, FD&C Red No. 3, FD&C Yellow No. 6, Gelatin NF, Lactose NF, Sodium Lauryl Sulfate NF and Silicon Dioxide NF.
• Dibenzyline is N-(2-Chloroethyl)-N-(1-methyl-2-phenoxyethyl)benzylamine hydrochloride:

This image is provided by the National Library of Medicine.

• Phenoxybenzamine hydrochloride is a colorless, crystalline powder with a molecular weight of 340.3, which melts between 136°and 141°C. It is soluble in water, alcohol and chloroform; insoluble in ether.

Pharmacodynamics

There is limited information regarding Pharmacodynamics of Phenoxybenzamine in the drug label.

Pharmacokinetics

• Twenty to 30 percent of orally administered phenoxybenzamine appears to be absorbed in the active form.
• The half-life of orally administered phenoxybenzamine hydrochloride is not known; however, the half-life of intravenously administered drug is approximately 24 hours. Demonstrable effects with intravenous administration persist for at least 3 to 4 days, and the effects of daily administration are cumulative for nearly a week.

Nonclinical Toxicology

• Case reports of carcinoma in humans after long-term treatment with phenoxybenzamine have been reported. Hence long-term use of phenoxybenzamine is not recommended. Carefully weigh the benefits and risks before prescribing this drug.

• Phenoxybenzamine hydrochloride showed in vitro mutagenic activity in the Ames test and mouse lymphoma assay; it did not show mutagenic activity in vivo in the micronucleus test in mice. In rats and mice, repeated intraperitoneal administration of phenoxybenzamine hydrochloride (three times per week for up to 52 weeks) resulted in peritoneal sarcomas. Chronic oral dosing in rats (for up to 2 years) produced malignant tumors of the small intestine and non-glandular stomach, as well as ulcerative and/or erosive gastritis of the glandular stomach. Whereas squamous cell carcinomas of the non-glandular stomach were observed at all tested doses of phenoxybenzamine hydrochloride, there was a no-observed-effect-level of 10 mg/kg for tumors (carcinomas and sarcomas) of the small intestine. This dose is, on a body surface area basis, about twice the maximum recommended human dosage of 20 mg b.i.d.

Clinical Studies

There is limited information regarding Clinical Studies of Phenoxybenzamine in the drug label.

How Supplied

• Dibenzyline (phenoxybenzamine hydrochloride) capsules, 10 mg, in bottles of 100 (NDC 65197-001-01).
• Store at 25°C (77°F); excursions permitted to 15°- 30°C (59°- 86°F).

Storage

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

Images

Drug Images

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Package and Label Display Panel

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Patient Counseling Information

There is limited information regarding Patient Counseling Information of Phenoxybenzamine in the drug label.

Precautions with Alcohol

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

Brand Names

• Dibenzyline®

Look-Alike Drug Names

• A® — B®

Drug Shortage Status

Price

References

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

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