Phentolamine

Phentolamine is a short-acting a-blocker that produces peripheral vasodilatation by blocking both a1- and a2-adrenergic receptors. Pulmonary vascular resistance and pulmonary arterial pressure are decreased.

Uses
Severe hypertension associated with phaeochromocytoma

Contraindications
Hypotension

Administration
Available in 10-mg ampoules
• IV bolus: 2–5 mg, repeat PRN
• IV infusion: 0.1–2 mg/min

Dilute in sodium chloride 0.9% or glucose 5% Monitor pulse and BP continuously

How not to use phentolamine
Do not use adrenaline, ephedrine, isoprenaline or dobutamine to treat phentolamine-induced hypotension (B2 effect of these sympathomimetics will predominate causing a further paradoxical ↓ BP) Treat phentolamine-induced hypotension with noradrenaline

Adverse effects
Hypotension
Tachycardia and arrhythmias
Dizziness
Nasal congestion

Cautions
Asthma (sulphites in ampoule may lead to hypersensitivity)
IHD