phentolamine mesylate
phentolamine mesylate
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.
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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.
See 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.