Calculated the half life for this drug? - 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 03-31-2011
USMLE Forums Guru
 
Steps History: Not yet
Posts: 339
Threads: 94
Thanked 330 Times in 150 Posts
Reputation: 290
Drug Calculated the half life for this drug?

A new antiepileptic drug is being studied. The first test subject is determined to have a volume of distribution of 60 L for this drug and a renal clearance of 4 L/hour. What is the approximate half life of this drug in this patient?

A - 2 hours
B - 7.5 hours
C - 10 hours
D - 15 hours
E - 18 hours
Reply With Quote Quick reply to this message



  #2  
Old 03-31-2011
harlesmd's Avatar
USMLE Forums Guru
 
Steps History: 1+CK+CS
Posts: 390
Threads: 40
Thanked 365 Times in 144 Posts
Reputation: 375
Default

Cl = Vd x 0,67/half life
half life = Vd x 0.67/Cl = 60 x 0.67/4 = 10 hours

The answer is : C
__________________
Time is immortal when you believe on something...
Reply With Quote Quick reply to this message
The above post was thanked by:
aktorque (04-01-2011), Lena (06-26-2011), star123 (06-19-2011)
  #3  
Old 03-31-2011
dr-ahmed's Avatar
USMLE Forums Guru
 
Steps History: 1+CK+CS
Posts: 333
Threads: 61
Thanked 388 Times in 90 Posts
Reputation: 398
Default

B , 7.5 hrs
Reply With Quote Quick reply to this message
  #4  
Old 03-31-2011
USMLE Forums Newbie
 
Steps History: Not yet
Posts: 1
Threads: 0
Thanked 0 Times in 0 Posts
Reputation: 10
Default answer

Quote:
Originally Posted by earthpole View Post
A new antiepileptic drug is being studied. The first test subject is determined to have a volume of distribution of 60 L for this drug and a renal clearance of 4 L/hour. What is the approximate half life of this drug in this patient?

A - 2 hours
B - 7.5 hours
C - 10 hours
D - 15 hours
E - 18 hours
I think about 7,5 hours because 60/2=30 and half life--->30/4=7,5 H
Reply With Quote Quick reply to this message
  #5  
Old 03-31-2011
USMLE Forums Newbie
 
Steps History: Not yet
Posts: 1
Threads: 0
Thanked 0 Times in 0 Posts
Reputation: 10
Default

Quote:
Originally Posted by honour View Post
I think about 7,5 hours because 60/2=30 and half life--->30/4=7,5 H

Hey, why do we need to divide the vd by 2?
Reply With Quote Quick reply to this message
  #6  
Old 03-31-2011
dr_mhm's Avatar
USMLE Forums Guru
 
Steps History: 1+CK+CS
Posts: 460
Threads: 100
Thanked 233 Times in 147 Posts
Reputation: 243
Default

C. 10 hours. The initial formula was correct.
T1/2 = 0.7 x Vd/Cl
There's no need to divide by 2 ?!?
Reply With Quote Quick reply to this message
  #7  
Old 03-31-2011
bebix's Avatar
USMLE Forums Master
 
Steps History: 1+CK+CS+3
Posts: 1,357
Threads: 194
Thanked 3,259 Times in 881 Posts
Reputation: 3269
Default

First we know that:

k = 0.693 / t 1/2 ==> t 1/2 = 0.693 / k

and

Clearence = V * k ==> k = Clearence / V


then,

t 1/2 = ( 0.693 * V ) / Clearence ==> 0.693 * 60 / 4 = 10 aprox.

C - 10 hours
Reply With Quote Quick reply to this message
The above post was thanked by:
aktorque (04-01-2011)
  #8  
Old 04-01-2011
USMLE Forums Guru
 
Steps History: Step 1 Only
Posts: 487
Threads: 95
Thanked 1,458 Times in 356 Posts
Reputation: 1468
Arrow

Quote:
Originally Posted by bebix View Post
First we know that:

k = 0.693 / t 1/2 ==> t 1/2 = 0.693 / k

and

Clearence = V * k ==> k = Clearence / V


then,

t 1/2 = ( 0.693 * V ) / Clearence ==> 0.693 * 60 / 4 = 10 aprox.

C - 10 hours
Quote:
Originally Posted by harlesmd View Post
Cl = Vd x 0,67/half life
half life = Vd x 0.67/Cl = 60 x 0.67/4 = 10 hours

The answer is : C
Both of you are correct. Know the formula. You'll get easy calculation on the exam... easy points guys... know the formula.
Reply With Quote Quick reply to this message
The above post was thanked by:
bronchiole (04-02-2011), harlesmd (04-01-2011)



Reply

Tags
Pharmacology-, Step-1-Questions

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
How USMLE Scores are calculated? StepTaker General Topics Recommended Threads 13 1 Week Ago 05:26 PM
Half-life Calculation Question good_boy_1234 USMLE Step 1 Forum 6 01-07-2012 03:48 PM
Pay half now, half later on your Step 2 CK Review Course! DrInTraining USMLE Step 2 CK Forum 1 02-22-2011 05:39 AM
Research Drug Half Life? Yallah USMLE Step 1 Forum 3 04-19-2010 07:43 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)