Regitine Dosage

Generic name: phentolamine mesylate
Dosage form: for Injection, USP
Drug class: Miscellaneous cardiovascular agents

Medically reviewed by Drugs.com. Last updated on Apr 30, 2024.

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

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

1. Prevention or control of hypertensive episodes in the patient with pheochromocytoma.

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

During surgery, Regitine (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 Regitine is added to each liter of solution containing norepinephrine. The pressor effect of norepinephrine is not affected.

For Treatment: 5-10 mg of Regitine in 10 mL of saline is injected into the area of extravasation within 12 hours.

3. Diagnosis of pheochromocytoma — Regitine 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.

a. 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 48-72 hours, prior to the test. Antihypertensive drugs are withheld until blood pressure returns to the untreated, hypertensive level. This test is not performed on a patient who is normotensive.

Procedure

The patient is kept at rest in the supine position throughout the test, preferably in a quiet, darkened room. Injection of Regitine 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 Regitine 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.

Regitine 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 mmHg systolic and 25 mmHg diastolic. A typical positive response is a reduction in pressure of 60 mmHg systolic and 25 mmHg diastolic. Usually, maximal effect is evident within 2 minutes after injection. A return to preinjection pressure commonly occurs within 15-30 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 mmHg systolic and 25 mmHg diastolic after injection of Regitine. 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.

b. Intramuscular

If the intramuscular test for pheochromocytoma is preferred, preparation is the same as for the intravenous test. Five milligrams of Regitine 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 30-45 minutes following injection. A positive response is indicated when the blood pressure is reduced 35 mmHg systolic and 25 mmHg diastolic, or more, within 20 minutes following injection.