Phenoxybenzamine HCl

A to Z Drug Facts

 Action Irreversibly blocks alpha-adrenergic receptors.

 Indications Control of episodes of hypertension and sweating in patients with pheochromocytoma. Unlabeled use(s): 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.

 Route/Dosage

ADULTS: PO 10 mg bid initially. Usual dosage range is 20 to 40 mg bid to tid. CHILDREN: PO 1 to 2 mg/kg/day in 3 to 4 divided doses.

 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.

 Lab Test Interferences None well documented.

 Adverse Reactions

CV: Orthostatic hypotension; tachycardia. CNS: Drowsiness; fatigue. EENT: Miosis. GI: Gastrointestinal irritation. GU: Inhibition of ejaculation. RESP: 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.

 Administration/Storage

• Give drug with milk or in divided doses to reduce GI irritation.
• Store in airtight container and protect from light.

 Assessment/Interventions

• Obtain patient history, including drug history and any known allergies.
• Instruct patient to change position slowly, especially from lying to sitting up or standing, and to dangle and move legs before standing.
• Assess for the following adverse reactions: Orthostatic hypotension, tachycardia, nasal congestion.
• Assess for effectiveness (lowering of BP) periodically.
• Take safety precautions if patient develops lightheadedness.
• If shocklike state develops, place patient in Trendelenburg position. Notify physician and begin emergency interventions.
• During dosage adjustments, monitor BP and pulse (eg, quality, rate, rhythm) with patient in lying and standing position for 4 days.
• In patients with peripheral vasospastic problems, observe for improvement in skin color, temperature, and quality of peripheral pulses.

 Patient/Family Education

• 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 physician.
• 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.

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Copyright © 2003 Facts and Comparisons
David S. Tatro
A to Z Drug Facts