Professional Drug Information > Phentolamine Mesylate

Phentolamine (Systemic)

VA CLASSIFICATION
Primary: AU105
Secondary: CV150; CV900 CV409


Note: For information pertaining to use of phentolamine for impotence, see Phentolamine (Intracavernosal).

Commonly used brand name(s): Rogitine.

Note: For a listing of dosage forms and brand names by country availability, see Dosage Forms section(s).



Category:


Antiadrenergic—

antihypertensive—

Indications

Note: Bracketed information in the Indications section refers to uses that are not included in U.S. product labeling.

Accepted

Hypertension, paroxysmal, in surgery for pheochromocytoma (prophylaxis and treatment)—Phentolamine is indicated to prevent or control paroxysmal hypertension prior to and during surgery for pheochromocytoma.^{02}

Necrosis, dermal (prophylaxis and treatment)—Parenteral phentolamine is indicated to prevent or treat dermal necrosis and sloughing following intravenous administration or extravasation of norepinephrine.^{02}

Unaccepted
Although phentolamine is indicated as an aid in the diagnosis of pheochromocytoma, determinations of blood and urine catecholamine concentrations are considered safer and more reliable.^{02}


Pharmacology/Pharmacokinetics

Physicochemical characteristics:
Molecular weight—
    377.46^{02}

Mechanism of action/Effect:

Hypertension—Alpha-adrenergic blockade (alpha ₁ and alpha ₂ receptors) and antagonism of effects of circulating epinephrine and norepinephrine to cause vasodilation and reduction in peripheral resistance. Phentolamine has little effect on the blood pressure of healthy individuals or patients with essential hypertension. ^{02}


Other actions/effects:

Phentolamine has direct positive inotropic and chronotropic effects on cardiac muscle.^{02}

Half-life:

Intravenous—Approximately 19 minutes ^{02}.

Elimination:
    Not completely known; however, approximately 13% of a single intravenous dose is excreted in urine as unmetabolized drug ^{02}.


Precautions to Consider

Carcinogenicity/Mutagenicity

Studies have not been done ^{02}.

Pregnancy/Reproduction

Pregnancy—
Adequate and well-controlled studies in humans have not been done.

Studies in rats and mice at oral doses of 24 to 30 times the usual daily human dose (based on a 60-kg human) found that phentolamine causes slightly decreased growth and slight skeletal immaturity (increased incidence of incomplete or unossified calcanei and phalangeal nuclei of the hind limb and of incompletely ossified sternebrae) in the fetuses. Studies in rats at oral doses of 60 times the usual daily human dose found a slightly lower implantation rate. Embryonic or fetal development was not affected in rabbits at oral doses of 20 times the usual daily human dose. No teratogenicity or embryotoxicity was found in rat, mouse, or rabbit studies. ^{02}

FDA Pregnancy Category C.

Breast-feeding

It is not known whether phentolamine is distributed into breast milk ^{02}. However, problems in humans have not been documented.

Pediatrics

Appropriate studies on the relationship of age to the effects of phentolamine have not been performed in the pediatric population. However, pediatrics-specific problems that would limit the usefulness of this medication in children are not expected.


Geriatrics


No information is available on the relationship of age to the effects of phentolamine in geriatric patients. However, the risk of phentolamine-induced hypothermia may be increased in elderly patients.

Drug interactions and/or related problems
The following drug interactions and/or related problems have been selected on the basis of their potential clinical significance (possible mechanism in parentheses where appropriate)—not necessarily inclusive (» = major clinical significance):


Note: Combinations containing any of the following medications, depending on the amount present, may also interact with this medication.


» Epinephrine    (concurrent use of epinephrine with phentolamine may block the alpha-adrenergic effects of epinephrine, possibly resulting in severe hypotension and tachycardia^{02})


Medical considerations/Contraindications
The medical considerations/contraindications included have been selected on the basis of their potential clinical significance (reasons given in parentheses where appropriate)— not necessarily inclusive (» = major clinical significance).


Risk-benefit should be considered when the following medical problems exist
» Angina ^{02} or
» Coronary artery insufficiency or disease ^{02} or
» Myocardial infarction, or history of ^{02}    (reflex tachycardia may precipitate frank congestive heart failure and angina; use of phentolamine is not recommended by the manufacturer)


Sensitivity to phentolamine ^{02}


Side/Adverse Effects

Note: Parenteral administration of phentolamine has been associated with acute and prolonged hypotension, tachycardia, cardiac arrhythmias, myocardial infarction, and cerebrovascular spasm or occlusion; deaths have been reported.

The following side/adverse effects have been selected on the basis of their potential clinical significance (possible signs and symptoms in parentheses where appropriate)—not necessarily inclusive:

Those indicating need for medical attention
Incidence more frequent
    
Reflex tachycardia^{02} (fast or irregular heartbeat)

Incidence less frequent
    
Cardiac arrhythmias^{02}
    
orthostatic hypotension^{02} ( chills or cold sweats ; confusion or fainting; dizziness or light-headedness, especially when getting up from a lying or sitting position)—may represent an acute hypotensive episode

Incidence rare
—most frequent after parenteral administration    
Cerebrovascular spasm or occlusion^{02} (confusion, severe or sudden headache, sudden loss of coordination, sudden slurring of speech )
    
myocardial infarction^{02} (chest pain, sudden shortness of breath)



Those indicating need for medical attention only if they continue or are bothersome
Incidence more frequent
    
Abdominal pain^{02}
    
diarrhea^{02}
    
nausea or vomiting
    
weakness^{02}

Incidence less frequent
    
Flushing or redness of face^{02}
    
nasal stuffiness^{02}





Overdose
For more information on the management of overdose or unintentional ingestion, contact a poison control center (see Poison Control Center Listing).

Clinical effects of overdose
The following effects have been selected on the basis of their potential clinical significance (possible signs and symptoms in parentheses where appropriate)—not necessarily inclusive:

Cardiovascular disturbances, such as
arrhythmias
hypotension
shock or
tachycardia

diarrhea

excitation

headache

hypoglycemia

nausea and vomiting

pupillary contraction

sweating

visual disturbances

Treatment of overdose
There is no specific antidote for phentolamine overdose.

Decreases in blood pressure to dangerous levels or other symptoms of shock should be treated immediately.

Treatment of acute hypotension —Elevate patient's legs and administer a plasma expander if necessary. Intravenous norepinephrine may be administered and titrated to maintain blood pressure at the normotensive levels. Supportive care should be available as necessary. Epinephrine is not recommended since it may cause a further paradoxical decrease in blood pressure.^{02}


Parenteral Dosage Forms

Note: Bracketed uses in the Dosage Forms section refer to categories of use and/or indications that are not included in U.S. product labeling.

PHENTOLAMINE MESYLATE INJECTION USP

Usual adult dose
Prevention and treatment of dermal necrosis and sloughing
During intravenous administration of norepinephrine: 10 mg added to each liter of intravenous fluid containing norepinephrine. ^{02}

Following extravasation of intravenous fluids containing norepinephrine: Infiltration, 5 to 10 mg in 10 mL of sodium chloride injection; effective only if given within twelve hours after extravasation. ^{02}

Hypertension, paroxysmal, in surgery for pheochromocytoma (prophylaxis and treatment)
Preoperative: Intravenous or intramuscular, 5 mg one to two hours before surgery, repeated if necessary. ^{02}

During surgery (to prevent or control symptoms of excessive epinephrine release due to manipulation of the tumor): Intravenous, 5 mg ^{02}as needed, adjusted according to response.


Usual pediatric dose
Hypertension, paroxysmal, in surgery for pheochromocytoma (prophylaxis and treatment)
Preoperative: Intramuscular or intravenous, 1 mg one to two hours before surgery; may be repeated if necessary.^{02}

During surgery (to prevent symptoms of excessive epinephrine release due to manipulation of the tumor): Intravenous, 1 mg as needed, adjusted according to response.^{02}


Size(s) usually available:
U.S.—


5 mg (Rx)[Generic]^{03}

Canada—


5 mg (Rx) [Rogitine]

Packaging and storage:
Store below 40 °C (104 °F), preferably between 15 and 30 °C (59 and 86 °F), unless otherwise specified by manufacturer.

Preparation of dosage form:
Phentolamine Mesylate for Injection USP is reconstituted for parenteral use by adding 1 mL of sterile water for injection to the vial, producing a solution containing 5 mg of phentolamine mesylate per mL.

Stability:
It is recommended that any unused portion be discarded ^{02}.

Revised: 07/17/2000

References

Note: All references used in the development and earlier revisions of this monograph have not yet been incorporated into the computer database and, therefore, are not listed below. Citations for information not yet referenced in the monograph will be provided upon request.

1. Not Used.
   

2. Product Information: Regetine, phentolamine. Novartis Pharmaceuticals, East Hanover, NJ, USA (PI revised 6/98) reviewed 2/2000.
   

3. Personal Communication: Catalano DJ, Associate Director, Mature Products Portfolio. Novartis Pharmaceuticals Corporation, East Hanover, NJ, May 31, 2000.
   

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