Phentolamine Dosing for Alpha-Adrenergic Receptor Toxicity
For alpha-adrenergic receptor toxicity, phentolamine should be administered as an IV bolus dose of 5 mg for adults (1 mg for children), which can be repeated every 10 minutes as needed to lower blood pressure to target. 1
Adult Dosing
- IV bolus: 5 mg initially 1
- Additional bolus doses can be given every 10 minutes as needed to control blood pressure 1
- Used specifically for hypertensive emergencies induced by catecholamine excess (pheochromocytoma, interactions between monoamine oxidase inhibitors and other drugs or food, cocaine toxicity, amphetamine overdose, or clonidine withdrawal) 1
Pediatric Dosing
- IV/IM: 0.1-0.2 mg/kg up to a maximum of 10 mg 1
- For children with pheochromocytoma: 1 mg IV/IM 2
- Dilute in 10 mL of 0.9% sodium chloride when used for extravasation 1
Administration for Extravasation
- For treatment of extravasation: 5-10 mg of phentolamine mesylate in 10 mL of saline injected into the area of extravasation within 12 hours 2
- For prevention of extravasation injury: 10 mg of phentolamine mesylate can be added to each liter of solution containing norepinephrine 2
Clinical Considerations
- Phentolamine is a non-selective alpha-adrenergic receptor antagonist that blocks both alpha-1 and alpha-2 receptors 3
- Particularly effective for hypertensive crises caused by catecholamine excess 1
- Onset of action is rapid when administered intravenously 4
- Monitor blood pressure continuously during administration due to risk of hypotension 1
- For extravasation of vasopressors (epinephrine, norepinephrine, dopamine), phentolamine should be administered as soon as possible to prevent tissue necrosis 1
Potential Adverse Effects
- Hypotension may occur, especially with rapid administration 1
- Reflex tachycardia 1
- Flushing and headache 3
- Arrhythmias 1
Special Populations
- In elderly patients, start at the lower end of the dosing range due to potential for increased sensitivity to hypotensive effects 1
- Use with caution in patients with coronary artery disease as rapid blood pressure reduction may precipitate myocardial ischemia 1
Remember that phentolamine is specifically indicated for hypertensive emergencies induced by catecholamine excess, and its use should be accompanied by appropriate hemodynamic monitoring 1.