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#1
12-11-2011
 USMLE Forums Guru Steps History: --- Posts: 332 Threads: 48 Thanked 170 Times in 109 Posts
Drug dose calculation questions

Normally, acetaminophen has a Vd =70L and CI = 350 mUmin. If acetaminophen was administered to a patient with 50% renal function, what parameter would differ from normal?

B. Maintenance dose would be higher
C. t 1/2 would be shorter
D. Vd would be 35L
E. Cl would be 700 mUmin

At 6 h after IV administration of bolus dose, the plasma level of a drug is 5 mgli. If the Vd = 10 L and the elimination half-life == 3 h, what was the dose administered?

A. l00 mg
B. 150 mg
C. 180 mg
D. 200 mg
E. 540 mg

Pls note that these two questions are not related.

Last edited by usluipek; 12-11-2011 at 07:36 PM.

#2
12-12-2011
 USMLE Forums Guru Steps History: 1 + CS Posts: 388 Threads: 48 Thanked 237 Times in 128 Posts Reputation: 247

Hmm. The loading dose doesnt change. MD decreases. Vd shud not change. N same goes for half life. So only option left z E. Tho i still dpnt understand how xan xlearance increase??!
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 The above post was thanked by: usluipek (12-12-2011)
#3
12-12-2011
 USMLE Forums Guru Steps History: 1 + CS Posts: 388 Threads: 48 Thanked 237 Times in 128 Posts Reputation: 247

2nd question. I suck at maths n fprmulas. But acc to Vd= dose / conc in plasma.. Anser shud b 10 * 5= 50! Which z not evn on the option!! So i dunno. But temme the answerzz!!
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#4
12-12-2011
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1) I didnt find any correct answer..

2) 150 mg (b)
Since passed 2 half lives, it was 15 mg concentration when the drug was administred, 10 = x/15 = 150 mg... am I right?
 The above post was thanked by: usluipek (12-12-2011)
#5
12-12-2011
 USMLE Forums Guru Steps History: --- Posts: 332 Threads: 48 Thanked 170 Times in 109 Posts

Hi, jriella,

For the first question, the book's answer is B, but I do not quite understand why it is B, because the maintenance dose should be lower.

For the second question, can you tell me how you get to this conclusion?
#6
12-12-2011
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Probably, there's a mistake with the alternatives..

Thinking again, I dont think that I did it right... dont know how to answer ;(
#7
12-12-2011
 USMLE Forums Guru Steps History: --- Posts: 332 Threads: 48 Thanked 170 Times in 109 Posts

Quote:
 Originally Posted by jriella Probably, there's a mistake with the alternatives.. Thinking again, I dont think that I did it right... dont know how to answer ;(
Your answer is right on the second one, but I just would like to know how you got the answer.
#8
12-12-2011
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 791 Threads: 76 Thanked 673 Times in 317 Posts Reputation: 691

Quote:
 Originally Posted by jriella 1) I didnt find any correct answer.. 2) 150 mg (b) Since passed 2 half lives, it was 15 mg concentration when the drug was administred, 10 = x/15 = 150 mg... am I right?
for 2nd question, after 6 hrs of administration its 5 mg. after 3 hrs it should be 10mg and at the time of administration it should be 20mg. hence ans s 200mg dose.
#9
12-13-2011
 USMLE Forums Guru Steps History: 1 + CS Posts: 300 Threads: 22 Thanked 97 Times in 62 Posts Reputation: 107

E and D

-when ur kidney doesnt work then the clearance decrease
-tow halflives back from 5 is 20

 Tags Pharmacology-, Step-1-Questions

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