Conceptual Question - 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 01-03-2012
USMLE Forums Veteran
 
Steps History: Not yet
Posts: 281
Threads: 74
Thanked 131 Times in 68 Posts
Reputation: 141
Default Conceptual Question

Drug X maximally increases aretiolar Resistance by 50% at a dose of 20 mg/ml. Drug Y increases arteolar resistance by 75% at dose of 40 mg/ml. What is the inference?

a. Drug X is has smaller volume of distribution
b. Drug X has smaller half life
c. Drug X is less efficacious
d. Drug X is less potent
e. Drug X has less LD50 than Y

Kindly post answer with reasoning why each option is wrong
Reply With Quote Quick reply to this message
The above post was thanked by:
step_enhancer (01-04-2012)



  #2  
Old 01-03-2012
Dr. Mexito's Avatar
USMLE Forums Master
 
Steps History: 1+CK+CS
Posts: 662
Threads: 72
Thanked 363 Times in 202 Posts
Reputation: 373
Default This is what I think...

a. I think this is the correct answer. Because with a higher volume distribution the more of the drug is needed to cause its effect. Drug X just needed 20 mg/mL to increase 50% of vascular resistance. So it means that is it may not be well distributed around the body.

b. I think that from the question we cannot know about the half life of both the drugs

c. Efficacy is the ability of a drug to elicit a response when interacts with a receptor: is the number of drug-receptor complexes that are formed. I do not know how we can know this from the question.

d. I think drug X is more potent: just 20 mg/mL to cause a 50% increase in the vascular resistance.

e. The question does not mention the therapeutic index, that would be used to know the risk of intoxication of drug X and Y. So I think this is also not true.

Well, I think is like this... I think I will wait for the correct answer...
__________________
"Disease is very old, and nothing about it has changed. It is we who change as we learn to recognize what was formerly imperceptible." JMC

Last edited by Dr. Mexito; 01-03-2012 at 11:46 PM.
Reply With Quote Quick reply to this message
  #3  
Old 01-04-2012
USMLE Forums Veteran
 
Steps History: Not yet
Posts: 281
Threads: 74
Thanked 131 Times in 68 Posts
Reputation: 141
Default

Thats not the correct ans.
Reply With Quote Quick reply to this message
  #4  
Old 01-04-2012
USMLE Forums Master
 
Steps History: 1+CK+CS
Posts: 851
Threads: 88
Thanked 706 Times in 379 Posts
Reputation: 716
Default

The answer is C.

the maximum effect of a drug can be produced- is efficacy.clearly Drug X can maximally increase arteriolar resistance by only 50% while drug Y can 75%

so drug Y has more efficacy .

to understand clearly see Vmax curve in pharma.lower Vmax lower efficacy.

LD50 Vd and T1/2 cannot be determined.

potency is the amount of drug needed for a given effect.we do not know what amt of drug required for DRUG Y to cause 50 % increase in resistance.

lets see if anyone will add something to this....
Reply With Quote Quick reply to this message
The above post was thanked by:
indigo (01-04-2012)
  #5  
Old 01-04-2012
USMLE Forums Veteran
 
Steps History: Not yet
Posts: 281
Threads: 74
Thanked 131 Times in 68 Posts
Reputation: 141
Default

Thats the correct ans C.

I was wondering since drug Y shows 75% resistance at 40 mg, would it cause 75/2=37.5% resistance at 20 mg concentration? This would mean that drug Y is more potent than X.

Or am I thinking completely wrong??
Reply With Quote Quick reply to this message
  #6  
Old 01-04-2012
USMLE Forums Master
 
Steps History: 1+CK+CS
Posts: 851
Threads: 88
Thanked 706 Times in 379 Posts
Reputation: 716
Default

Quote:
Originally Posted by indigo View Post
Thats the correct ans C.

I was wondering since drug Y shows 75% resistance at 40 mg, wont it cause 75/2=37.5% resistance at 20 mg concentration? This would mean that drug Y is more potent than X.

Or am I thinking completely wrong??
the maximum effect attain is efficacy(irrespective of the dose)

look at the Vmax curve the top of curve that coincides to the Y-axis is the efficacy.

drug X causes 50% constriction while drug Y can cause 75% constriction
drug Y has more efficacy.
Reply With Quote Quick reply to this message
  #7  
Old 01-04-2012
USMLE Forums Veteran
 
Steps History: Not yet
Posts: 281
Threads: 74
Thanked 131 Times in 68 Posts
Reputation: 141
Default

So you mean there is no way to compare the potency of the drugs in this case.
Reply With Quote Quick reply to this message
  #8  
Old 01-04-2012
USMLE Forums Master
 
Steps History: 1+CK+CS
Posts: 851
Threads: 88
Thanked 706 Times in 379 Posts
Reputation: 716
Default

Quote:
Originally Posted by indigo View Post
So you mean there is no way to compare the potency of the drugs in this case.
in this Q i dont think u ca compare potency.the potency option is distractor.

but in competitive inhibition of enzyme,more substrate is req to get the same amt of effect so there ,the potency is decreased.
i dont think in this Q potency can be compared.
but enough info is given to compare efficacy so Q can be solved.
Reply With Quote Quick reply to this message
The above post was thanked by:
indigo (01-04-2012), mohitkmc (01-04-2012)
  #9  
Old 01-04-2012
USMLE Forums Veteran
 
Steps History: Not yet
Posts: 281
Threads: 74
Thanked 131 Times in 68 Posts
Reputation: 141
Default

You are right potency cannot be compared as they need to give the concentrations at which both the drugs have same effect or, the effects of both the drugs at the same concn to compare potency
Man sometimes i feel i am not a Doc but a Physicist or something
Reply With Quote Quick reply to this message
  #10  
Old 01-04-2012
USMLE Forums Master
 
Steps History: 1+CK+CS
Posts: 851
Threads: 88
Thanked 706 Times in 379 Posts
Reputation: 716
Default

dont sweat it .this stuff is confusing nobody gets it in the first time.
i m good at mathematics kind of stuff like physics
but suck at cramming stuff and i m finding so much cramming is req for step 1 too.like micro n pharma i hope everything goes well..
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
question help: diabetic foot related question dezirablize USMLE Step 2 CK Forum 5 01-15-2015 03:42 PM
My Step 1 Results; (257/88); Exam is conceptual not First Aid Based! yasirsattar75 USMLE Step 1 Forum 36 01-12-2012 07:44 PM
Set Question list/Different Question for each CC tbk568 USMLE Step 2 CS Forum 0 12-13-2011 02:47 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)