phentolamine mesylate

phentolamine mesylate, (fentol´mēn´ mes´ilāt´),

n brand name: Regitine;
drug class: antihypertensive;
action: α-adrenergic blocker; binds to α-adrenergic receptors, dilating peripheral blood vessels, lowering peripheral resistance, lowering blood pressure;
uses: hypertension, pheochromocytoma, prevention and treatment of dermal necrosis following extravasation of norepinephrine or dopamine.

---

phentolamine mesylate

Regitine, Rogitine (CA) (UK)

Pharmacologic class: Alpha-adrenergic blocker

Therapeutic class: Diagnostic agent, antihypertensive agent in pheochromocytoma

Pregnancy risk category C

Action

Competitively blocks postsynaptic (alpha₁) and presynaptic (alpha₂) adrenergic receptors. Acts on arterial tree and venous bed, reducing total peripheral resistance and lowering venous return to heart.

Availability

Powder for injection: 5 mg

⊘Indications and dosages

➣ To prevent or control hypertensive episodes before or during pheochromocytomectomy

Adults: 5 mg I.V. or I.M. 1 to 2 hours before surgery, then 5 mg I.V. during surgery as indicated

Children: 1 mg I.V. or I.M. 1 to 2 hours before surgery, then 1 mg I.V. during surgery as indicated

➣ To aid pheochromocytoma diagnosis

Adults: 2.5 or 5 mg (in 1 ml of sterile water) by I.V. injection; record blood pressure q 30 seconds for 3 minutes, then q minute for next 7 minutes. Or 5 mg (in 1 ml sterile water) I.M.; record blood pressure q 5 minutes for 30 to 45 minutes.

➣ To prevent or treat dermal necrosis after norepinephrine extravasation

Adults: For prevention, add 10 mg to each liter of I.V. solution containing norepinephrine. For treatment, inject 5 to 10 mg in 10 ml of normal saline solution into extravasated area within 12 hours.

Off-label uses

• Hypertensive crisis caused by MAO inhibitors
• Rebound hypertension caused by withdrawal of clonidine, propranolol, or other antihypertensives
• Erectile dysfunction (given with papaverine)

Contraindications

• Hypersensitivity to drug
• Coronary artery disease
• Myocardial infarction (MI) or history of MI
• Coronary insufficiency
• Angina

Precautions

Use cautiously in:
• patients receiving cardiac glycosides concurrently
• pregnant or breastfeeding patients.

Administration

• Reconstitute powder by diluting with 1 ml of sterile water for injection.
• For pheochromocytoma diagnosis, withhold sedatives, analgesics, and nonessential drugs for 24 to 72 hours before test (until hypertension returns). Keep patient supine until blood pressure stabilizes; then rapidly inject drug I.V. Maximum effect usually occurs within 2 minutes of dosing.

Route	Onset	Peak	Duration
I.V., I.M.	Immediate	Unknown	Brief

Adverse reactions

CNS: weakness, dizziness

CV: tachycardia, acute and prolonged hypotension, orthostatic hypotension, arrhythmias

EENT: nasal congestion

GI: nausea, vomiting, diarrhea

Skin: flushing

Interactions

Drug-drug. Ephedrine, epinephrine: antagonism of these drugs' effects

Drug-herbs. Ephedra (ma huang): antagonism of vasoconstrictive effects

Patient monitoring

• When using for norepinephrine extravasation, monitor injection site closely and assess blood pressure, heart rate, and respiratory rate.
• For pheochromocytoma diagnosis, monitor blood pressure. In pheochromocytoma, systolic and diastolic pressures drop immediately and steeply. Monitor and record blood pressure immediately after injection, at 30-second intervals for first 3 minutes, and at 1-minute intervals for next 7 minutes. Systolic decrease of 60 mmHg and diastolic decrease of 25 mmHg within 2 minutes after I.V. administration indicates a positive reaction for pheochromocytoma.

Patient teaching

• Explain drug administration procedure.
☞ Instruct patient to promptly report adverse reactions. Assure him he'll be monitored closely.
• Tell patient to withhold other drugs (especially sedatives and analgesics) for at least 24 hours before pheochromocytoma testing, if appropriate.
• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs and herbs mentioned above.