Phentolamine

Mechanism of action:

It competitively blocks α adrenergic receptors. It causes inhibition to the response to serotonin.

It causes weak activation of the muscarinic receptors in GI tract and H1 and H2 histaminic receptors in the stomach.

Action:
It causes vasodilatation by

1. Blocking α adrenergic receptors

2. Nonadrenergic activity on vascular smooth muscles

This causes a decrease in peripheral vascular resistance and elevated venous capacitance.

It causes cardiac stimulation through blockade of α2 adrenergic receptors and reflex effect.

It also causes stimulation of salivary, lacrimal, pancreatic and respiratory tract secretions.

Pharmacokinetics:
It has a relatively short duration of action.

Therapeutic uses:
It is used effectively in the diagnosis of Pheochromocytoma and hypertensive crisis caused by Pheochromocytoma.

It is also used in Raynaud’s phenomenon and frost bite.

It is also used for erectile dysfunction.

It can be used to prevent dermal necrosis.

Adverse effects:
It may cause severe tachycardia, angina pectoris, arrhythmia and diarrhea.

Precautions:
It should be used with caution in patients with
1. Peptic ulcer
2. Coronary artery disease