Corrected dose in impaired renal function - 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 01-17-2012
patho2012's Avatar
USMLE Forums Veteran
 
Steps History: ---
Posts: 213
Threads: 13
Thanked 119 Times in 81 Posts
Reputation: 129
Drug Corrected dose in impaired renal function

Gentamicin is sometimes given in intermittent intravenous bolus doses of 100mg 3 times a day to achieve target peak plasma concentrations of about 5 mg/L. Gentamicin clearance (normally 5.4L/h/70kg) is almost entirely by glomerular filtration. Your patient, however, is found to have a Creatine clearance 1/3 of normal. Your initial dosage regimen for this pt would probably be:
(A) 20mg 3 times/day
(B) 33mg 3 times/day
(C) 72 mg 3 times/day
(D) 100 mg 2 times/day
(E) 150 mg 2 times/day

+explanation, plz.
Reply With Quote Quick reply to this message



  #2  
Old 01-17-2012
Hitman's Avatar
USMLE Forums Master
 
Steps History: Not yet
Posts: 928
Threads: 17
Thanked 539 Times in 375 Posts
Reputation: 549
Default

i think the ans would be D ..... Loading dose in not changed in renal impairment , but maintenance dose decreases , thus 150 twice would achieve the target conc level ....
Reply With Quote Quick reply to this message
  #3  
Old 02-08-2012
USMLE Forums Newbie
 
Steps History: Not yet
Posts: 2
Threads: 0
Thanked 0 Times in 0 Posts
Reputation: 10
Default

MD = Cl x Cp / F = Cl x Css x dosing interval



Cp, F & Css are absolutely constant variables.
I don't think it is a good idea to chang dosing interval, so just consider it as a constant variable too.


Gentamicin clearance is mainly glomerular filtration, so, if creatine clearance = GFR = 1/3 of normal level, Cl of Gentamicin = 1/3 of normal level.

So MD should be 1/3 of normal level.

The answer is 33.

Hopefully, i am right
Reply With Quote Quick reply to this message
 
  #4  
Old 02-08-2012
USMLE Forums Scout
 
Steps History: Not yet
Posts: 36
Threads: 5
Thanked 8 Times in 6 Posts
Reputation: 18
Default

MD=Cp x CL/F
So,what is changed here?Only CL,how?timed 1/3.So the dose needed in a healthy individual will be timed 1/3 too,giving us 100mg/d.

B) I guess.
Reply With Quote Quick reply to this message
  #5  
Old 02-08-2012
Hitman's Avatar
USMLE Forums Master
 
Steps History: Not yet
Posts: 928
Threads: 17
Thanked 539 Times in 375 Posts
Reputation: 549
Default

Quote:
Originally Posted by patho2012 View Post
Gentamicin is sometimes given in intermittent intravenous bolus doses of 100mg 3 times a day to achieve target peak plasma concentrations of about 5 mg/L. Gentamicin clearance (normally 5.4L/h/70kg) is almost entirely by glomerular filtration. Your patient, however, is found to have a Creatine clearance 1/3 of normal. Your initial dosage regimen for this pt would probably be:
(A) 20mg 3 times/day
(B) 33mg 3 times/day
(C) 72 mg 3 times/day
(D) 100 mg 2 times/day
(E) 150 mg 2 times/day

+explanation, plz.
i guess they are asking for Loading dose , which doesnot change with renal impairment ...... but they confused us by not putting 100 by 3 in the option so every one would just divide by 3 and make it a perfect 33 by 3 ...
so i think it would be 150 by 2 which equals to 100 by 3 !!!
Reply With Quote Quick reply to this message
  #6  
Old 02-08-2012
USMLE Forums Newbie
 
Steps History: Not yet
Posts: 2
Threads: 0
Thanked 0 Times in 0 Posts
Reputation: 10
Default

LD normally refers to the intial single dose. I really never see LD given by BID or TID.

And it really doesn't make sense to me that if someone has renal dysfunction and we increase the dose.

So I think it makes more sense if we calculate the MD here

Last edited by Charlotte; 02-08-2012 at 05:32 PM.
Reply With Quote Quick reply to this message
  #7  
Old 02-08-2012
Hitman's Avatar
USMLE Forums Master
 
Steps History: Not yet
Posts: 928
Threads: 17
Thanked 539 Times in 375 Posts
Reputation: 549
Default

Quote:
Originally Posted by Charlotte View Post
LD normally refers to the intial single dose. I really never see LD given by BID or TID.

And it really doesn't make sense to me that if someone has renal dysfunction and we increase the dose.

So I think it makes more sense if we calculate the MD here
yes agreed LD is usually given as a single dose , but the Qs says Gentamicin is sometimes given in intermittent intravenous bolus doses of 100mg 3 times a day to achieve target peak plasma concentrations of about 5 mg/L

LD is generally given to achieve a initial target concentration specially in drugs like gentamycin ..... and its not increasing the dose its the same dose 100 by 3 is 300 and 150 by 2 is 300 .... ... i feel its a tricky way of giving the same option of 100 by 3 ... so when you dont find this in the options you simply divide it by 3 and select 33 by 3 ........
Reply With Quote Quick reply to this message
  #8  
Old 02-11-2012
Master shifu's Avatar
USMLE Forums Addict
 
Steps History: Step 1 Only
Posts: 191
Threads: 14
Thanked 87 Times in 59 Posts
Reputation: 97
Default

If the drug is cleared entirely by the kidney and creatinine clearanceis reduced to 1/3rd of normal,the total daily dose should also be reduced to 1/3rd.
So the answer is definitely B i.e. 33mg 3 times per day
Reply With Quote Quick reply to this message



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
impaired defence mechanisms DrAa USMLE Step 2 CK Forum 3 04-12-2016 01:22 PM
pt with impaired vision qurat21 USMLE Step 2 CK Forum 6 02-09-2012 01:44 AM
Drug of choice for Hypertension in an asthmatic, hyperkalemic, renal impaired patient! alaahoda2001 USMLE Step 1 Forum 15 09-24-2011 05:38 AM
Kid with swollen eye, chemosis, decreased motion, and impaired vision! usmleman2020 USMLE Step 1 Forum 10 08-06-2011 06:32 AM
Impaired level of consciousness DrSeddik USMLE Step 1 Forum 3 12-01-2009 01:36 PM

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)