Phentolamine

Injection
Dermal necrosis associated with norepinephrine IV infusion

Intravenous
Hypertension in phaeochromocytoma

Parenteral
Diagnosis of pheochromocytoma

Renal impairment, coronary or cerebral arteriosclerosis, concurrent use with phosphodiesterase-5 (PDE-5) inhibitors including sildenafil (>25 mg), tadalafil, or vardenafil.

Tachycardia or history of cardiac arrhythmias; gastritis or peptic ulcer disease; pregnancy and lactation. Discontinue if symptoms of angina occur or worsen.

Orthostatic hypotension, tachycardia, flushing, sweating, feelings of apprehension, anginal pain, arrhythmias, nausea, vomiting, diarrhoea, weakness, dizziness, nasal congestion.
Potentially Fatal: MI, cerebrovascular spasm or occlusion.

IM/IV/Parenteral: C

Hypoglycaemia; severe hypotension, tachycardia, vomiting, dizziness. If fluid replacement is inadequate to treat hypotension, only alpha-adrenergic vasopressors such as norepinephrine should be used. Mixed agents such as epinephrine may cause more hypotension.

Epinephrine, ephedrine: effects may be decreased; ethanol: increased toxicity (disulfiram reaction).
Potentially Fatal: Additive BP-lowering effects with sildenafil, tadalafil or vardenafil.

Description: 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.
Onset: IM: 15-20 min; IV: immediate.
Duration: IM: 30-45 min; IV: 15-30 min.
Pharmacokinetics:
Metabolism: Hepatic.
Excretion: Metabolism: Hepatic. Via urine (10% as unchanged drug); half-life elimination: 19 min.

The reconstituted solution should be used upon preparation and should not be stored. Store unopened vials at controlled room temperature (59-86°F).

Other Antihypertensives