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#1
03-19-2014
 USMLE Forums Newbie Steps History: Step 1 Only Posts: 2 Threads: 1 Thanked 0 Times in 0 Posts Reputation: 10
pharmacology question :: drug elimination

drug A is elimination 60% by kidney. If GFR decrease 50%, new dose muse be?
A. 40%
B. 50%
C. 60%
D. 70%

#2
03-19-2014
 USMLE Forums Scout Steps History: Not yet Posts: 25 Threads: 4 Thanked 4 Times in 3 Posts Reputation: 14

It can be done like this.

Let the normal dose be X.

Now here we have 60% elimination by kidney and 40% by rest.
But now, the GFR has been reduced to 50%.
So the new dose can be calculated as

New dose= 0.4*X + 0.6*X*( patient's GFR/Normal GFR which is considered 100%)
New Dose= 0.4*X + 0.6*X*(0.5)
= 0.4*X +0.3*X
=0.7*X

So the new dose is 70% of the original dose. Hence option D is correct.
#3
03-19-2014
 USMLE Forums Newbie Steps History: Step 1 Only Posts: 2 Threads: 1 Thanked 0 Times in 0 Posts Reputation: 10

#4
03-19-2014
 USMLE Forums Scout Steps History: Not yet Posts: 25 Threads: 4 Thanked 4 Times in 3 Posts Reputation: 14

Hopefully it helped you.

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