Phenoxybenzamine Hydrochloride

Pronunciation: fen-ox-ee-BEN-zuh-meen HIGH-droe-KLOR-ide
Class: Agent for pheochromocytoma

Trade Names

Dibenzyline
- Capsules 10 mg

Pharmacology

Irreversibly blocks alpha-adrenergic receptors.

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Pharmacokinetics

Absorption

20% to 30% of an oral dose is absorbed in the active form.

Metabolism

Phenoxybenzamine hydrochloride metabolism is hepatic.

Elimination

Phenoxybenzamine hydrochloride excretion is renal and biliary. The t 1/ 2 is approximately 24 h (IV); oral is unknown.

Duration

3 to 4 days (IV).

Indications and Usage

Control of episodes of hypertension and sweating in patients with pheochromocytoma.

Unlabeled Uses

Treatment of micturition disorders resulting from neurogenic bladder; treatment of functional outlet obstruction and partial prostatic obstruction.

Contraindications

Conditions in which fall in BP may be undesirable.

Dosage and Administration

Adults

PO 10 mg bid initially. Usual dosage range is 20 to 40 mg 2 to 3 times daily.

Children

PO 1 to 2 mg/kg/day in 3 to 4 divided doses.

Storage/Stability

Store in airtight container and protect from light.

Drug Interactions

Epinephrine

Exaggerated hypotensive response and tachycardia may occur when epinephrine, or other agents that stimulate both alpha- and beta-receptors, are given concomitantly with phenoxybenzamine.

Laboratory Test Interactions

None well documented.

Adverse Reactions

Cardiovascular

Orthostatic hypotension; tachycardia.

CNS

Drowsiness; fatigue.

EENT

Miosis.

GI

GI irritation.

Genitourinary

Inhibition of ejaculation.

Respiratory

Nasal congestion.

Precautions

Pregnancy

Safety not established.

Lactation

Undetermined.

Special Risk Patients

Administer drug with caution to patients with marked cerebral or coronary arteriosclerosis or renal damage. Adrenergic blocking effects may aggravate respiratory infections.

Overdosage

Symptoms

Orthostatic hypotension, dizziness, fainting, tachycardia, vomiting, lethargy, shock.

Patient Information

  • Advise patient to avoid alcoholic beverages.
  • Stress to patient importance of weight reduction, sodium and alcohol restriction, discontinuation of smoking, regular exercise, and behavior modification.
  • Instruct patient to avoid OTC cough, cold, or allergy medications containing sympathomimetics without consulting health care provider.
  • Instruct patient to avoid sudden position changes to prevent orthostatic hypotension. Warn patient that taking a hot bath or shower may aggravate dizziness.
  • Inform patient that drug may cause nasal congestion and constricted pupils.
  • Advise patient that inhibition of ejaculation may occur, but reassure patient that this condition generally decreases with continued therapy.
  • Advise patient that drug may cause drowsiness, and to use caution while driving or performing other tasks requiring mental alertness.

Copyright © 2009 Wolters Kluwer Health.

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