PHENTOLAMINE

“REGITINE”

1) Therapeutic drug action & mechanism(pharmacology)

• Alpha blocker

• Potent competitive antagonist of a-receptors [both a1 & a2]

• Suppresses pressor activity of circulating catecholamines

• Causes a drop in SVR: i) a-receptors blockade

ii) direct action on vascular smooth muscle

2) Indications

• Afterload reduction for CCF; left ventricular failure post MI

• Note: GTN & SNP have largely replaced phentolamine due to their ease in administration and higher potency

• Peripheral vascular disorders, phaeochromocytoma

3) Effects on organs—side effects

• Tachycardia : i) reflex via baroreceptors

ii) a2-receptor blockade

4) Toxic effects/ precautions with administration

5) Contraindications

6) Reversal, antagonism or antidote

• Noradrenaline, not adrenaline, should be given for overdose associated hypotension [will exacerbate tachycardia]

7) Loading dose, maintenance dose, frequency & method of administration

• 10 mg/1ml ampoule

• Give 5mg bolus iv

8) Drug’s metabolism—Drug’s excretion—Half life (pharmacokinetics)

9) Important drug interactions