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Old 08-27-2012
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Default nbme 11 question doubt!!

cud sm1 pls tel me d correct answer to dis questn frm nbme 1??

d one wt d graph shown dose response curves of 2 drugs, X and Y..drug Y alone has no effect..but wt X it shifts graph to rit at low concentratns n decrease d efficacy at higher concentrations..n d questn is wich of s following describe drug Y??
A)competitive reversibl antagonist
B)full agonist
C)inverse agonist
D)noncomp antagonist
E)partial agonist

if ny1 of u remembr dis questn n knw d answer pls do tel me!! tnx
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  #2  
Old 08-27-2012
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I don't understand quite well what u wrote and neither remember this question. But what I know is that if your efficacy is decreased then you are moving the curve down and you are dealing with a noncompetitive antagonist. But if you are saying that the curve have moved down and to the right then you are dealing with a partial agonist because you are decreasing the efficacy thus the Vmax (maximal velocity for the reaction) and can either increased or decreased the potency, if you are saying that is moving to the right then you are decreasing your potency thus increasing your km (concentration of substrate at 1/2 of Vmax)
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Old 08-27-2012
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D-Noncompetitive Antagonist

This is the case on the concept of "Spare Receptors"

Assume ...100% receptor occupancy required by an Agonist to exert Maximum Effect (Emax) /Optimal effect.

and now consider, if Emax is achieved with result

*Efficacy of Drug X decreases
*5 of the spare receptors are still Unoccupied

Now if we raise the drug "X" dosage.....it will bind to the remaining unoccupied spare receptors and brings it Efficacy back to to the Emax.

there for "No Change in Efficacy" , only "Potency decreases"(as needed higher dose of Drug X)


---------------------------------Graph on the Right--------------------------

But at "High Dose" of of NCA (Drug Y), it will bind to e.g all the 10 spare receptors---->result

*Efficacy(Emax) of Drug X decreases
*there are non of the spare receptors left unoccupied

since there are no extra receptors left, even if we raise the Drug "X" dosage, it won't be able to increase it's Efficacy back to Emax.

hope this will help u....
http://www.usmleforum.com/files/foru...1/586776-8.php
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Matched!!!
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Old 08-28-2012
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im sry anomali, bt i didnt quite undrstand!! does dat mean dat a non-competitive inhibitor intially kinda acts lik a competitive inhibitor at lower cocentrations??cz d efficacy remains maximal by increasn dose of substrate??
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