Q.why use of competitive antagonist has no change in efficacy & Vmax? - USMLE Forums
USMLE Forums Logo
USMLE Forums         Your Reliable USMLE Online Community     Members     Posts
Home
USMLE Articles
USMLE News
USMLE Polls
USMLE Books
USMLE Apps
Go Back   USMLE Forums > USMLE Step 1 Forum

USMLE Step 1 Forum USMLE Step 1 Discussion Forum: Let's talk about anything related to USMLE Step 1 exam


Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 08-25-2015
USMLE Forums Addict
 
Steps History: ---
Posts: 137
Threads: 62
Thanked 3 Times in 3 Posts
Reputation: 13
Default Q.why use of competitive antagonist has no change in efficacy & Vmax?

Q. Why competitive antagonist brings no change in efficacy and no effect on Vmax? My understanding is- if antagonist will bind to the receptor site where agonist normally binds, the effect (efficacy) of the agonist should be decreased,isn't it? .Next, about Vmax, when competitive antagonist goes and blocks the the active site of the enzyme where substrate/agonist would normally bind, wouldn't it decrease the reaction rate (Vmax) since enzyme is not working normally in this case due to binding of competitive antagonist?

I know I am missing some concepts here.Can anybody pls help me out to understand this.Thanks. (from:FA, enzyme kinetics & pharmacodynamics)
Reply With Quote Quick reply to this message



  #2  
Old 08-25-2015
USMLE Forums Addict
 
Steps History: ---
Posts: 137
Threads: 62
Thanked 3 Times in 3 Posts
Reputation: 13
Default

Wanted to add one example to my above question.

If flumazenil (competitive antagonist of diazepam) doesn't decreases the efficacy (effect) of the diazepam, why then it used as an antidote of diazepam overdose? But, again it is said that use of competitive antagonist has no change in efficacy and Vmax. My understanding is in contrast to what is mentioned in book. Need sb's assistance.
Reply With Quote Quick reply to this message
  #3  
Old 08-25-2015
CleverFOX's Avatar
USMLE Forums Veteran
 
Steps History: Step 1 Only
Posts: 239
Threads: 4
Thanked 176 Times in 116 Posts
Reputation: 188
Send a message via Skype™ to CleverFOX
Default

Well yeah it's called Vmax... Max....

It means the max that can be achieved....

With competitive antagonists we actually block the receptors with weak bonds...the bonds can be easily broken if we increase the conc of the agonist itself!

So although it decreases or hampers the activities of the agonist it doesn't do it permanently...ie it's competitive! We add more agonist and the receptor will do its job at its max potential!

But in case of non competitive antagonist they bind and destroy a receptor for good...so if we are destroying receptors we are decreasing the tissues maximum ability to receive signals and act...

But in the previous case we only tried to mess up the receptors for a temporary time being! So no effect on Vmax!
Reply With Quote Quick reply to this message
The above post was thanked by:
Aumsai (08-25-2015)
 
  #4  
Old 08-25-2015
USMLE Forums Addict
 
Steps History: ---
Posts: 137
Threads: 62
Thanked 3 Times in 3 Posts
Reputation: 13
Default

Thanks cleverfox.That means, only when we increase the concentration of agonist, we can reverse the efficacy and Vmax (not altering the efficacy/Vmax). But, if we do not increase the concentration of agonist (keep the concentration of agonist constant), then efficacy and Vmax will remain decreased,right?So, I don't think it is 100% accurate to say -"Competitive antagonist doesn't change efficacy & Vmax".Maybe it is more accurate to say,competitive antagonist decreases efficacy/vmax until agonist are added;after addition of competitive antagonist , the efficacy/Vmax will be back to its former value.What do u say?Do u agree with me?
Reply With Quote Quick reply to this message
  #5  
Old 08-25-2015
CleverFOX's Avatar
USMLE Forums Veteran
 
Steps History: Step 1 Only
Posts: 239
Threads: 4
Thanked 176 Times in 116 Posts
Reputation: 188
Send a message via Skype™ to CleverFOX
Default

Like I said it's v max.... MAX is the word....

And you should remember that we are dealing with the receptor action and not the concentration of the drug when using the term max....

So when we are talking Vmax we mean unlimited agonists stimulating the functional receptors.... So you can assume to keep conc constant
Reply With Quote Quick reply to this message
The above post was thanked by:
Aumsai (08-25-2015)
  #6  
Old 08-25-2015
USMLE Forums Addict
 
Steps History: ---
Posts: 137
Threads: 62
Thanked 3 Times in 3 Posts
Reputation: 13
Default

ok, got it. Thanks man.
Reply With Quote Quick reply to this message



Reply

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the USMLE Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:
Medical School
Choose "---" if you don't want to tell. AMG for US & Canadian medical schools. IMG for all other medical schools.
USMLE Steps History
What steps finished! Example: 1+CK+CS+3 = Passed Step 1, Step 2 CK, Step 2 CS, and Step 3.

Choose "---" if you don't want to tell.

Favorite USMLE Books
What USMLE books you really think are useful. Leave blank if you don't want to tell.
Location
Where you live. Leave blank if you don't want to tell.

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes


Similar Threads
Thread Thread Starter Forum Replies Last Post
Competitive versus Non-Competitive; Reversible versus Irreversible Antagonism anomali USMLE Step 1 Forum 15 04-06-2017 03:49 AM
DA antagonist wa87el USMLE Step 1 Forum 0 07-30-2014 02:43 PM
Competitive versus Non-Competitive Antagonism? CHAKRAM USMLE Step 1 Forum 3 04-24-2013 05:01 AM
Drug dose, half life, and efficacy adeelacheema USMLE Step 1 Forum 4 07-16-2012 02:30 AM
Enzyme kinetics: competitive vs. non-competitive inhibition jackat1000 USMLE Step 1 Mnemonics 0 01-22-2010 09:15 AM

RSS Feed
Find Us on Facebook
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.

USMLE® & other trade marks belong to their respective owners, read full disclaimer
USMLE Forums created under Creative Commons 3.0 License. (2009-2014)