Phentolamine

A to Z Drug Facts

(fen-TOLE-uh-meen)

Regitine,  Rogitine

Class: Antihypertensive/Agent for pheochromocytoma

 Action Decreases total peripheral resistance and venous return to heart by competitive blockade of presynaptic and postsynaptic alpha-adrenergic receptors.

 Indications Prevention or control of hypertensive episodes in patients with pheochromocytoma; pharmacologic test for pheochromocytoma (not method of choice); prevention and treatment of dermal necrosis and sloughing following IV administration or extravasation of norepinephrine or dopamine. Unlabeled use(s): Control of hypertensive crises secondary to MAO inhibitor-sympathomimetic amine interactions or withdrawal of clonidine, propranolol or other antihypertensives; in conjunction with papaverine as intracavernous injection for impotence.

 Contraindications Hypersensitivity to phentolamine or related compounds; MI, coronary insufficiency, angina, or other evidence suggestive of coronary artery disease.

 Route/Dosage

Hypertensive Episodes in Pheochromocytoma

ADULTS: IM/IV 5 mg 1 to 2 hr before surgery. Repeat if necessary. During surgery, IV 5 mg as indicated. CHILDREN: IM/IV 1 mg 1 to 2 hr before surgery. During surgery, IV 1 mg as indicated.

Prevention of Dermal Necrosis and Sloughing

ADULTS: IV Add 10 mg/1 L of solution containing norepinephrine.

Treatment of Dermal Necrosis or Sloughing After Norepinephrine Extravasation

ADULTS: 5 to 10 mg in 10 ml saline solution in area of extravasation within 12 hr. CHILDREN: Infiltrate area 0.1 to 0.2 mg/kg (maximum 10 mg).

Diagnosis of Pheochromocytoma

ADULTS: IV/IM 2.5 to 5 mg. CHILDREN: IV 1 mg or IM 3 mg.

 Interactions

Epinephrine, ephedrine: Vasoconstricting and hypertensive effects of epinephrine and ephedrine are antagonized by phentolamine.

 Lab Test Interferences None well documented.

 Adverse Reactions

CV: Acute and prolonged hypotensive episodes; tachycardia; cardiac arrhythmias; orthostatic hypotension. CNS: Weakness; dizziness. EENT: Nasal stuffiness. GI: Nausea; vomiting; diarrhea. OTHER: Flushing.

 Precautions

Pregnancy: Category C. Lactation: Undetermined. Cardiovascular effects: Marked hypotensive episodes and shocklike states may follow use of phentolamine and lead to MI, cerebrovascular spasm, or cerebrovascular occlusion. Screening tests: Urinary assays of catecholamines or other biochemical assays have largely supplanted phentolamine and other pharmacologic tests for pheochromocytoma. Phentolamine is usually used as confirmation. Follow specific guidelines for use of phentolamine.

 Administration/Storage

• Have patient remain supine during IV therapy.
• Dilute 5 mg in 1 ml Sterile Water for Injection. May dilute further with 5 to 10 ml Sterile Water for Injection.
• Use reconstituted solution immediately; do not store.
• Store unopened vial in light-resistant container at room temperature.
• When using phentolamine for managing hypertensive crisis or as a diagnostic test, inject drug by rapid IV bolus.

 Assessment/Interventions

• Obtain patient history, including drug history and any known allergies.
• Obtain baseline lying and standing BP and pulse before starting therapy.
• Assess IV site for infiltration.
• Monitor BP every 2 min when beginning IV therapy until BP is stable.
• Notify physician immediately if symptoms of severe hypotension or shock develop.
• If chest pain develops during infusion, notify physician.
• If patient develops dizziness, take safety precautions (eg, bed in low position, supervise ambulation).

 Patient/Family Education

• Instruct patient to avoid sudden position changes to prevent orthostatic hypotension.
• Instruct patient to notify physician if chest pain develops during infusion.
• Tell patient to report the following symptoms to physician: Dizziness, fainting spells or weakness.

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