No

Alpha₁ Blockers

Diagnosis of pheochromocytoma and treatment of hypertension associated with pheochromocytoma or other caused by excess sympathomimetic amines; as treatment of dermal necrosis after extravasation of drugs with alpha-adrenergic effects (norepinephrine, dopamine, epinephrine, dobutamine)

C

Hypersensitivity to phentolamine or any component; renal impairment; coronary or cerebral arteriosclerosis

Myocardial infarction, cerebrovascular spasm and cerebrovascular occlusion have occurred following administration. Use with caution in patients with gastritis or peptic ulcer, tachycardia, or a history of cardiac arrhythmias.

Cardiovascular: Hypotension, tachycardia, arrhythmia, flushing, orthostatic hypotension

Central nervous system: Weakness, dizziness

Gastrointestinal: Nausea, vomiting, diarrhea

Respiratory: Nasal congestion

Case report: Pulmonary hypertension

Symptoms of overdose include tachycardia, shock, vomiting, dizziness

Hypotension and shock should be treated with fluids and by placing the patient in the Trendelenburg position; only alpha-adrenergic pressors such as norepinephrine should be used; mixed agents such as epinephrine, may cause more hypotension. Take care not to cause so much swelling of the extremity or digit that a compartment syndrome occurs.

Epinephrine, ephedrine: Effects may be decreased.

Ethanol: Increased toxicity (disulfiram reaction).

Reconstituted solution is stable for 48 hours at room temperature and 1 week when refrigerated

Competitively blocks alpha-adrenergic receptors to produce brief antagonism of circulating epinephrine and norepinephrine to reduce hypertension caused by alpha effects of these catecholamines; also has a positive inotropic and chronotropic effect on the heart

Onset of action: I.M.: Within 15-20 minutes; I.V.: Immediate

Duration: I.M.: 30-45 minutes; I.V.: 15-30 minutes

Metabolism: In the liver

Half-life: 19 minutes

Elimination: Urine (10% as unchanged drug)

Treatment of alpha-adrenergic drug extravasation: S.C.:

Children: 0.1-0.2 mg/kg diluted in 10 mL 0.9% sodium chloride infiltrated into area of extravasation within 12 hours

Adults: Infiltrate area with small amount of solution made by diluting 5-10 mg in 10 mL 0.9% sodium chloride within 12 hours of extravasation

If dose is effective, normal skin color should return to the blanched area within 1 hour

Diagnosis of pheochromocytoma: I.M., I.V.:

Children: 0.05-0.1 mg/kg/dose, maximum single dose: 5 mg

Adults: 5 mg

Surgery for pheochromocytoma: Hypertension: I.M., I.V.:

Children: 0.05-0.1 mg/kg/dose given 1-2 hours before procedure; repeat as needed every 2-4 hours until hypertension is controlled; maximum single dose: 5 mg

Adults: 5 mg given 1-2 hours before procedure and repeated as needed every 2-4 hours

Hypertensive crisis: Adults: 5-20 mg

Blood pressure, heart rate

LFTs rarely

May cause dizziness

Concurrent use with psychotropics may produce additive hypotension; treatment of choice for hypertensive crisis secondary to MAOIs

Although the alpha-adrenergic blocking effects could antagonize epinephrine, there is no information available to require special precautions

No effects or complications reported

Immediately report pain at infusion site. Report any dizziness, feelings of faintness, or palpitations. Do not change position rapidly; rise slowly or ask for assistance. Pregnancy/breast-feeding precautions: Inform prescriber if you are or intend to be pregnant. Consult prescriber if breast-feeding.

Monitor patient for orthostasis; assist with ambulation

Injection, as mesylate: 5 mg/mL (1 mL)

Cooper BE, "High-Dose Phentolamine for Extravasation of Pressors," Clin Pharm, 1989, 8(10):689.

Gould L, Reddy CV, Chua W, et al, "Electrophysiological Properties of Phentolamine in Man," Br Heart J, 1977, 39(9):939-44.

Hollander JE, Carter WA, and Hoffman RS, "Use of Phentolamine for Cocaine-Induced Myocardial Ischemia," N Engl J Med, 1992, 327(5):361.

Roberts JR and Krisanda TJ, "Accidental Intra-Arterial Injection of Epinephrine Treated With Phentolamine," Ann Emerg Med, 1989, 18(4):424-5.

Seino S, Seino Y, Taminato T, et al, "Effect of Adrenergic Blocking Agents on Plasma Gastrin and Secretion Levels in Man," Am J Gastroenterol, 1980, 73(2):137-40.

Wespes E, Rondeux C, and Schulman CC, "Effect of Phentolamine on Venous Return in Human Erection," Br J Urol, 1989, 63(1):95-7.