phentolamine mesylate


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Related to phentolamine mesylate: Regitine

phentolamine mesylate

Rogitine (CA) (UK)

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.

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.

phentolamine mesylate, (fentol´əmēn´ 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.
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