Phentolamine is non selective reversible alpha blocker, histamine agonist (H1, H2) and muscarinic agonist. It also has inhibitory effects at serotonin receptors.
Oral absorption is unpredictable. Peak plasma levels are observed after 1 hour. Half life is 5-7 hours.
Used in pheocytochroma.
Its adverse affects include cardiac stimulation, postural hypertension, reflex tachycardia, headache, arrhythmias, diarrhea and palpitations.