Calculating the steady state concentration of Drug X - USMLE Forums
 USMLE Forums         Your Reliable USMLE Online Community     Members     Posts
 Home USMLE Articles USMLE News USMLE Polls USMLE Books USMLE Apps
 USMLE Forums Calculating the steady state concentration of Drug X
 User Name Remember Me? Password
 Register FAQs Members List Search Today's Posts Mark Forums Read

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

 Thread Tools Search this Thread Display Modes
#1
01-25-2012
 USMLE Forums Addict Steps History: Not yet Posts: 124 Threads: 13 Thanked 60 Times in 43 Posts Reputation: 70
Calculating the steady state concentration of Drug X

A pharmacy fellow is trying to determine what the plasma concentration of an experimental antiarrhythmic agent (Drug X) will be at steady-state. A continuous intravenous infusion of the agent began 6 hours earlier at a rate of 3 mg/min. Drug X has a half-life of 3 hours, a volume of distribution of 120 L, and a clearance of 0.6 L/min. If the rate of infusion remains constant, what will the plasma concentration be at steady-state?

A. 0.005 mg/L
B. 0.4 mg/L
C. 2.0 mg/L
D. 5.0 mg/L
E. 40.0 mg/L
F. 200.0 mg/L
 The above post was thanked by: docusmle9 (01-26-2012), step_enhancer (01-25-2012), strive (1 Week Ago), zainsyed (05-01-2014)

#2
01-25-2012
 USMLE Forums Master Steps History: Not yet Posts: 928 Threads: 17 Thanked 539 Times in 375 Posts Reputation: 549

Ans D........

infusion rate = Css * Cl ( clearance )

thus Css = infusion rate / clearance

3/0.6 = 5 mg/ml .......

god i am bad at these ........
 The above post was thanked by: Moloch (01-26-2012), step_enhancer (01-25-2012)
#3
01-26-2012
 USMLE Forums Addict Steps History: Not yet Posts: 191 Threads: 8 Thanked 121 Times in 76 Posts Reputation: 131

The given infusion rate is a maintanence dose so I agree with @ Hitman using the formula answer is D. 5

#4
01-26-2012
 USMLE Forums Master Steps History: 1+CK+CS Posts: 1,406 Threads: 118 Thanked 647 Times in 409 Posts Reputation: 657

D. 5

MD = (Cl x Css x infusion rate) / bioavailability
3 = (0.6 x Css x 1) / 1
3 = 0.6 x Css
Css = 3 / 0.6
Css = 5
__________________
"inflammable means flammable!? What a country."
#5
01-26-2012
 USMLE Forums Addict Steps History: Not yet Posts: 124 Threads: 13 Thanked 60 Times in 43 Posts Reputation: 70

yup!!!! u guys r rite.
the ans is....... DDDDD.... 5.0mg/L
 The above post was thanked by: docusmle9 (01-26-2012), Moloch (01-26-2012)
#6
04-15-2013
 USMLE Forums Scout Steps History: Not yet Posts: 13 Threads: 4 Thanked 3 Times in 3 Posts Reputation: 13

Quote:
 Originally Posted by Dr.NickRiviera D. 5 MD = (Cl x Css x infusion rate) / bioavailability 3 = (0.6 x Css x 1) / 1 3 = 0.6 x Css Css = 3 / 0.6 Css = 5

MD=Cl x Css x DOSING INTERVAL ( not infusion rate) / f
#7
11-08-2016
 USMLE Forums Newbie Steps History: --- Posts: 1 Threads: 0 Thanked 0 Times in 0 Posts Reputation: 10
steady state concentration

I have a more or less equal problem.

I want to calculate the Css with only know the urine concentration (0,5µg/l) and the half life time (60days).

It is a toxin that everybody takes up during the day by inhalation. So the Problem is that everybody takes up a different dose.

Has somebody any idea?

 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.
 AMG IMG ---
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.

 Not yet Step 1 Only CK Only CS Only 1 + CK 1 + CS 1+CK+CS CK+CS 1+CK+CS+3 ---
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

 User Name Remember Me? Password
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 Linear Mode

 Similar Threads Thread Thread Starter Forum Replies Last Post usluipek USMLE Step 1 Forum 12 03-07-2016 10:24 PM INCOGNITO USMLE Step 1 Forum 5 10-14-2011 09:26 PM aktorque USMLE Step 1 Forum 9 02-15-2011 06:35 AM usluipek USMLE Step 1 Forum 6 02-01-2011 07:45 PM good_boy_1234 IMG Residency Match Forum 5 09-09-2010 05:57 AM

 Home - Contact Us - Forum Rules - Advertise - Mobile Site - Archive - Privacy Statement - Top
 Follow @usmleforums
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)

 Terms of Use