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Phentolamine Mesylate for Injection

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Phentolamine Mesylate for Injection

INDICATIONS

Phentolamine Mesylate (phentolamine mesylate) for Injection is indicated for the prevention or control of hypertensive episodes that may occur in a patient with pheochromocytoma as a result of stress or manipulation during preoperative preparation and surgical excision.

Phentolamine Mesylate (phentolamine mesylate) for Injection is indicated for the prevention or treatment of dermal necrosis and sloughing following intravenous administration or extravasation of norepinephrine.

Phentolamine Mesylate (phentolamine mesylate) for Injection is also indicated for the diagnosis of pheochromocytoma by the phentolamine blocking test.

DOSAGE AND ADMINISTRATION

The reconstituted solution should be used upon preparation and should not be stored.

1. Prevention or control of hypertensive episodes in the patient with pheochromo-cytoma.

For preoperative reduction of elevated blood pressure, 5 mg of phentolamine mesylate (phentolamine mesylate) (1 mg for children) is injected intravenously or intramuscularly 1 or 2 hours before surgery, and repeated if necessary.

During surgery, phentolamine mesylate (phentolamine mesylate) (5 mg for adults, 1 mg for children) is administered intravenously as indicated, to help prevent or control paroxysms of hypertension, tachycardia, respiratory depression, convulsions, or other effects of epinephrine intoxication. (Postoperatively, norepinephrine may be given to control the hypotension that commonly follows complete removal of a pheochromocytoma.)

2. Prevention or treatment of dermal necrosis and sloughing following intravenous administration or extravasation of norepinephrine.

For Prevention: 10 mg of phentolamine mesylate (phentolamine mesylate) is added to each liter of solution containing norepinephrine. The pressor effect of norepinephrine is not affected.

For Treatment: 5 to 10 mg of phentolamine mesylate (phentolamine mesylate) in 10 mL of saline is injected into the area of extravasation within 12 hours.

3. Diagnosis of pheochromocytoma - phentolamine blocking test.

The test is most reliable in detecting pheochromocytoma in patients with sustained hypertension and least reliable in those with paroxysmal hypertension. False-positive tests may occur in patients with hypertension without pheochromocytoma.

Intravenous

Preparation

The CONTRAINDICATIONS, WARNINGS, and PRECAUTIONS sections should be reviewed. Sedatives, analgesics, and all other medications except those that might be deemed essential (such as digitalis and insulin) are withheld for at least 24 hours, and preferably 48 to 72 hours, prior to the test. Antihypertensive drugs are withheld until blood pressure returns to the untreated, hypertensive level. This test is not preformed on a patient who is normotensive.

Procedure

The patient is kept at rest in a supine position throughout the test, preferably in a quiet, darkened room. Injection of phentolamine is delayed until blood pressure is stabilized, as evidenced by blood pressure readings taken every 10 minutes for at least 30 minutes.

Five milligrams of phentolamine mesylate (phentolamine mesylate) is dissolved in 1 mL of Sterile Water for Injection. The dose for adults is 5 mg; for children, 1 mg.

The syringe needle is inserted into the vein, and injection is delayed until pressor response to venipuncture has subsided.

Phentolamine is injected rapidly. Blood pressure is recorded immediately after injection, at 30-second intervals for the first 3 minutes, and at 60-second intervals for the next 7 minutes.

Interpretation

A positive response, suggestive of pheochromocytoma, is indicated when the blood pressure is reduced more than 35 mm Hg systolic and 25 mm Hg diastolic. A typical positive response is a reduction in pressure of 60 mm Hg systolic and 25 mm Hg diastolic. Usually, maximal effect is evident within 2 minutes after injection. A return to preinjection pressure commonly occurs within 15 to 30 minutes but may occur more rapidly.

If blood pressure decreases to a dangerous level, the patient should be treated as outlined under OVERDOSAGE.

A positive response should always be confirmed by other diagnostic procedures, preferably by measurement of urinary catecholamines or their metabolites.

A negative response is indicated when the blood pressure is elevated, unchanged, or reduced less than 35 mm Hg systolic and 25 mm Hg diastolic after injection of phentolamine.

A negative response to this test does not exclude the diagnosis of pheochromocytoma, especially in patients with paroxysmal hypertension in whom the incidence of false-negative responses is high.

Intramuscular

If the intramuscular test for pheochromocytoma is preferred, preparation is the same as for the intravenous test. Five milligrams of phentolamine mesylate (phentolamine mesylate) is then dissolved in 1 mL of Sterile Water for Injection. The dose for adults is 5 mg intramuscularly; for children, 3 mg. Blood pressure is recorded every 5 minutes for 30 to 45 minutes following injection. A positive response is indicated when the blood pressure is reduced 35 mm Hg systolic and 25 mm Hg diastolic, or more, within 20 minutes following injection.

Note: Parenteral drug products should be inspected visually for particulate matter and discoloration prior to administration, whenever solution and container permit.

HOW SUPPLIED

Phentolamine Mesylate (phentolamine mesylate) for Injection USP, 5 mg, for intramuscular or intravenous use, is supplied in a 2 mL vial and individually boxed. NDC 55390-113-01.

The reconstituted solution should be used upon preparation and should not be stored.

Store at controlled room temperature, 15° to 30°C (59° to 86°F).

Manufactured for: Bedford Laboratories™ Bedford, OH 44146. Manufactured by: Ben Venue Laboratories™ Bedford, OH 44146. May 1999. FDA Rev date: 4/29/1999

Last reviewed on RxList: 10/21/2008
This monograph has been modified to include the generic and brand name in many instances.

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