Phentolamine
Indications
Phentolamine is used for:
Treatment of hypertension during pheochromocytoma surgery, Epinephrine or norepinephrine extravastation treatment, Diagnosis of pheochromocytoma
Adult Dose
Pheochromocytoma
Diagnosis: 5 mg IV/IM
Test for pheochromocytoma is positive if decrease SBP >35 mmHg & decrease DBP >25 mmHg
Pheochromocytoma Surgery Use
Treatment of hypertension during pheochromocytoma surgery
5 mg IV/IM 1-2 hr preoperative, repeat if necessary q2-4hr
Extravasation Treatment
Epinephrine or norepinephrine extravastation treatment
Treatment: 5-10 mg in 10 mL NS local injection within 12 hr
Prevention: 10 mg for each liter of IV fluids (pressor effect of NE is unaffected)
Child Dose
Pheochromocytoma, Diagnosis
0.1-0.2 mg/kg IV/IM, OR 1 mg IV OR 3 mg IM
Pheochromocytoma Surgery Use
Treatment of hypertension during surgery
0.05-0.1 mg/kg/dose OR 1 mg IV/IM 1-2 hr preoperative, repeat q2-4hr until hypertension is controlled; not to exceed 5 mg/dose
Renal Dose
Administration
IV Preparation
Reconstitute with 1 mL SWI (5 mg/mL solution)
IV/IM Administration
Administer by IV or IM injection
Rapid IV
Contra Indications
Renal impairment, coronary or cerebral arteriosclerosis, concurrent use with phosphodiesterase-5 (PDE-5) inhibitors including sildenafil (>25 mg), tadalafil, or vardenafil.
Precautions
First dose effect may occur, causing a sudden and drastic fall in blood pressure after administering the first dose.
Hypotension/syncope with first few doses or with increase in dose
Minimize by using small first dose at bedtime
Increase dose slowly
Pregnancy-Lactation
Pregnancy Category: C
Lactation: not known if excreted in breast milk; not recommended
Interactions
Epinephrine, ephedrine: effects may be decreased; ethanol: increased toxicity (disulfiram reaction).
Potentially Fatal: Additive BP-lowering effects with sildenafil, tadalafil or vardenafil.
Adverse Effects
Side effects of Phentolamine :
1-10%
Nasal congestion (10% )
Post-treatment pain (up to 10% )
Injection site pain (4% to 6% )
Diarrhea (<3% )
Frequency Not Defined
Cardiac dysrhythmia
Chest pain
Hypotension
Myocardial infarction
CVA - cerebrovascular accident due to cerebral artery occlusion
Mechanism of Action
Phentolamine is a reversible (competitive) and non-selective alpha-adrenergic receptor blocker, producing brief antagonism of circulating epinephrine and norepinephrine to reduce hypertension caused by alpha effects of these catecholamines. It has direct action on vascular smooth muscle; and has positive inotropic and chronotropic effects on the heart as well.