physio/pharm Q

[W19]

A 60-year-old man is scheduled to undergo surgical excision of a pheochromocytoma. He has history of episodes of severe HTN. An autonomic blocking agent is administered to control his HTN during the week prior to his surgical procedure. Which of the following agent is most appropriate?

A- a muscarinic blocker

B- a muscarinic agonist

C- a competitive alpha-blocker

D- a non-competitive alpha-blocker

E- an alpha agonist

.....Explain your answer because I am torn between two answer choices.

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[TOKOY90]

D. You want to administer something as phenoxybenzamine which is an alpha1 blocker, since alpha1 is responsible for vasoconstriction and since you have increased levels of epi you want to prevent your BP from going through the roof. It has to be a non-competetive blocker, since for competetive blockers at high concentrations of the substrate would displace the antagonist and still have an effect, and in pheo you would have high levels of E, hence competetive alpha blockers such that phentolamine would not be as effective.
hope this helps,
OK

 

[W19]

D. You want to administer something as phenoxybenzamine which is an alpha1 blocker, since alpha1 is responsible for vasoconstriction and since you have increased levels of epi you want to prevent your BP from going through the roof. It has to be a non-competetive blocker, since for competetive blockers at high concentrations of the substrate would displace the antagonist and still have an effect, and in pheo you would have high levels of E, hence competetive alpha blockers such that phentolamine would not be as effective.
hope this helps,
OK

That was my reasoning as well... Thanks!