A-Z Drug Facts > Phentolamine

Phentolamine

Pronouncation: (fen-TOLE-uh-meen)
Class: Agent for pheochromocytoma

Trade Names:
Phentolamine Mesylate
- Powder for Injection 5 mg (as mesylate)/vial

Rogitine (Canada)

Pharmacology

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

Pharmacokinetics

Absorption

Not determined.

Distribution

Not determined.

Metabolism

Not determined.

Elimination

Urine (13% as unchanged drug). T _1/2 is 19 min (IV).

Indications and Usage

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 Uses

Control of hypertensive crises secondary to MAOI-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.

Dosage and Administration

Hypertensive Episodes in Pheochromocytoma
Adults

IM / IV 5 mg 1 to 2 h before surgery. Repeat if necessary. During surgery, IV 5 mg as indicated.

Children

IM / IV 1 mg 1 to 2 h 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 h.

Children

Infiltrate area 0.1 to 0.2 mg/kg (max, 10 mg).

Diagnosis of Pheochromocytoma
Adults

IM / IV 2.5 to 5 mg.

Children

IV 1 mg or IM 3 mg.

General Advice

• 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.

Storage/Stability

Store unopened vials at controlled room temperature (59° to 86°F).

Drug Interactions

Epinephrine, ephedrine

Vasoconstrictive and hypertensive effects of epinephrine and ephedrine are antagonized by phentolamine.

Laboratory Test Interactions

None well documented.

Adverse Reactions

Cardiovascular

Acute and prolonged hypotensive episodes; tachycardia; cardiac arrhythmias; orthostatic hypotension.

CNS

Weakness; dizziness.

EENT

Nasal stuffiness.

GI

Nausea; vomiting; diarrhea.

Miscellaneous

Flushing.

Precautions

Pregnancy

Category C .

Lactation

Undetermined.

CV 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.

Overdosage

Symptoms

Severe hypotension, shock, tachycardia, flushing.

Patient Information

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

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