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Pronunciation
(fen oks ee BEN za meen)
Generic Available (U.S.)
No
Index Terms
Brand Names: U.S.
Pharmacologic Category
Pharmacologic Category Synonyms
Use: Labeled Indications
Symptomatic management of pheochromocytoma
Use: Unlabeled/Investigational
Micturition problems associated with neurogenic bladder, functional outlet obstruction, and partial prostate obstruction; treatment of hypertensive crisis caused by sympathomimetic amines
Pregnancy Risk Factor
C
Pregnancy Considerations
Adequate animal reproduction studies have not been conducted. It is not known whether phenoxybenzamine can cause fetal harm when administered to a pregnant woman or can affect reproduction capacity.
Lactation
Excretion in breast milk unknown/not recommended
Contraindications
Hypersensitivity to phenoxybenzamine or any component of the formulation; conditions in which a fall in blood pressure would be undesirable (eg, shock)
Warnings/Precautions
Concerns related to adverse effects:
• Cardiovascular effects: An exaggerated hypotensive response and tachycardia may occur when administered concurrently with compounds that stimulate both alpha- and beta-adrenergic receptors or in the setting of pheochromocytoma. Discontinue if symptoms of severe hypotension or angina occur.
Disease-related concerns:
• Obstructive atherosclerosis: Use with caution in patients with obstructive cerebral or coronary atherosclerosis, since a marked reduction in blood pressure may induce ischemic symptoms.
• Renal impairment: Use with caution in patients with renal impairment.
• Respiratory tract infection: Can exacerbate symptoms of respiratory tract infections.
Special populations:
• Elderly: Use with caution in the elderly; may be at higher risk of adverse effects.
Other warnings/precautions:
• Long-term use: Not recommended for long-term use due to case reports of cancer in humans.
Adverse Reactions
Frequency not defined.
Cardiovascular: Postural hypotension, tachycardia
Central nervous system: Drowsiness, fatigue
Gastrointestinal: GI irritation
Genitourinary: Inhibition of ejaculation
Ocular: Miosis
Respiratory: Nasal congestion
Metabolism/Transport Effects
None known.
Drug Interactions
Alpha1-Blockers: May enhance the antihypertensive effect of other Alpha1-Blockers. Risk X: Avoid combination
Amifostine: Antihypertensives may enhance the hypotensive effect of Amifostine. Management: When amifostine is used at chemotherapy doses, antihypertensive medications should be withheld for 24 hours prior to amifostine administration. If antihypertensive therapy can not be withheld, amifostine should not be administered. Risk D: Consider therapy modification
Antihypertensives: May enhance the hypotensive effect of other Antihypertensives. Risk C: Monitor therapy
Beta-Blockers: May enhance the orthostatic hypotensive effect of Alpha1-Blockers. The risk associated with ophthalmic products is probably less than systemic products. Exceptions: Levobunolol; Metipranolol. Risk D: Consider therapy modification
Calcium Channel Blockers: Alpha1-Blockers may enhance the hypotensive effect of Calcium Channel Blockers. Risk C: Monitor therapy
Diazoxide: May enhance the hypotensive effect of Antihypertensives. Risk C: Monitor therapy
Herbs (Hypertensive Properties): May diminish the antihypertensive effect of Antihypertensives. Risk C: Monitor therapy
Herbs (Hypotensive Properties): May enhance the hypotensive effect of Antihypertensives. Risk C: Monitor therapy
MAO Inhibitors: May enhance the orthostatic hypotensive effect of Orthostatic Hypotension Producing Agents. Risk C: Monitor therapy
Methylphenidate: May diminish the antihypertensive effect of Antihypertensives. Risk C: Monitor therapy
Pentoxifylline: May enhance the hypotensive effect of Antihypertensives. Risk C: Monitor therapy
Phosphodiesterase 5 Inhibitors: May enhance the hypotensive effect of Alpha1-Blockers. Management: Ensure patient is stable on alpha 1 blocker before starting PDE5 inhibitor; initiate PDE5 inhibitor at lowest possible dose. If patient stable on PDE5 inhibitor, initiate alpha 1 blocker at lowest dose. Avoid tadalafil with alpha 1 blockers for BPH. Risk D: Consider therapy modification
Prostacyclin Analogues: May enhance the hypotensive effect of Antihypertensives. Risk C: Monitor therapy
RiTUXimab: Antihypertensives may enhance the hypotensive effect of RiTUXimab. Risk D: Consider therapy modification
Yohimbine: May diminish the antihypertensive effect of Antihypertensives. Risk C: Monitor therapy
Ethanol/Nutrition/Herb Interactions
Ethanol: Avoid ethanol.
Herb/Nutraceutical: Avoid bayberry, blue cohosh, cayenne, ephedra, ginger, ginseng (American), kola, licorice, (may worsen hypertension). Avoid black cohosh, California poppy, coleus, golden seal, hawthorn, mistletoe, periwinkle, quinine, shepherd's purse (may have increased antihypertensive effect).
Storage
Store at controlled room temperature of 25°C (77°F).
Mechanism of Action
Produces long-lasting noncompetitive alpha-adrenergic blockade of postganglionic synapses in exocrine glands and smooth muscle; relaxes urethra and increases opening of the bladder
Pharmacodynamics/Kinetics
Duration: I.V.: ≥3 days
Bioavailability: 20% to 30%
Half-life elimination: I.V.: 24 hours
Dosage
Oral:
Children (unlabeled use): Initial: 0.25-1 mg/kg/day (maximum: 10 mg); increase slowly to blood pressure control
Adults:
Pheochromocytoma, hypertension: Initial: 10 mg twice daily; increase by 10 mg every other day until optimal blood pressure response is achieved; usual range: 20-40 mg 2-3 times/day. Doses up to 240 mg/day have been reported (Kinney, 2000).
Micturition disorders (unlabeled use): 10-20 mg 1-2 times/day
Administration: Oral
GI irritation may be reduced by giving in divided doses.
Monitoring Parameters
Blood pressure, pulse, urine output, orthostatics
Geriatric Considerations
Because of the risk of adverse effects, avoid the use of this medication in the elderly if possible.
Anesthesia and Critical Care Concerns/Other Considerations
Hypotensive effect may last for a few days after discontinuation.
Dental Health: Effects on Dental Treatment
Key adverse event(s) related to dental treatment: Xerostomia (normal salivary flow resumes upon discontinuation).
Dental Health: Vasoconstrictor/Local Anesthetic Precautions
No information available to require special precautions
Mental Health: Effects on Mental Status
May cause sedation, confusion, or dizziness
Mental Health: Effects on Psychiatric Treatment
Concurrent use with low potency antipsychotics, TCAs and MAO inhibitors may produce additive hypotension
Dosage Forms
Excipient information presented when available (limited, particularly for generics); consult specific product labeling.
Capsule, oral, as hydrochloride:
Dibenzyline®: 10 mg
Pricing: U.S. (www.drugstore.com)
Capsules (Dibenzyline)
10 mg (30): $255.99
Extemporaneously Prepared
A 2 mg/mL oral suspension may be made with capsules, propylene glycol 1%, and citric acid 0.15% in distilled water. Prepare the vehicle by dissolving 150 mg citric acid in a minimal amount of distilled water. Add 1 mL propylene glycol and mix well; add quantity of distilled water sufficient to make 10 mL. Grind the contents of two 10 mg capsules in a mortar and reduce to a fine powder. Add a small portion of the vehicle and mix to a uniform paste; transfer to a graduated cylinder, rinse mortar with vehicle, and add quantity of vehicle sufficient to make 10 mL. Transfer to an amber glass prescription bottle with tight-fitting cap; label "shake well" and "refrigerate". Stable for 7 days when stored in amber glass prescription bottles and refrigerated.
A stock solution of 10 mg/mL in propylene glycol was stable for 30 days refrigerated. When this stock solution was diluted 1:4 (v/v) with syrup (66.7% sucrose) to 2 mg/mL, the preparation was stable for 1 hour refrigerated. Note: Although the stock solution is stable for 30 days, it must be diluted before administration to decrease the amount of propylene glycol delivered to the patient.
Lim LY, Tan LL, Chan EW, et al, "Stability of Phenoxybenzamine Hydrochloride in Various Vehicles," Am J Health Syst Pharm, 1997, 54(18):2073-8.
References
Hack HA, “The Perioperative Management of Children With Phaeochromocytoma,” Paediatr Anaesth, 2000, 10(5):463-76.
Kinney MA, Narr BJ, and Warner MA, “Perioperative Management of Pheochromocytoma,” J Cardiothorac Vasc Anesth, 2002, 16(3):359-69.
Kinney MA, Warner ME, vanHeerden JA, et al, “Perianesthetic Risks and Outcomes of Pheochromocytoma and Paraganglioma Resection,” Anesth Analg, 2000, 91(5):1118-23.
Te AE, “A Modern Rationale for the Use of Phenoxybenzamine in Urinary Tract Disorders and Other Conditions,” Clin Ther, 2002, 24(6):851-61.
International Brand Names
Lexi-Comp.com
Last full review/revision October 2011
Content last modified October 2011
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