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#1
03-27-2013
 USMLE Forums Guru Steps History: 1+CK+CS Posts: 316 Threads: 17 Thanked 159 Times in 97 Posts Reputation: 169
Time to reach Drug Steady State

A constant infusion of drug Y is begun. Drug Y has a Volume of Distribution of 5L, and a clearance of 0.05L/h.

Aproximately how long would it take drug Y to reach steady state?

a. 70
b. 100
c. 112
d. 280
e. 400

 The above post was thanked by: fadi551 (03-29-2013), neha_subh (03-29-2013)

#2
03-27-2013
 USMLE Forums Addict Steps History: Not yet Posts: 125 Threads: 17 Thanked 67 Times in 38 Posts Reputation: 77

t1/2=0.7xVd/CL
0.7x5=3.5
3.5/0.05=70
70x4=280
 The above post was thanked by: neha_subh (03-28-2013)
#3
03-27-2013
 USMLE Forums Veteran Steps History: Step 1 Only Posts: 283 Threads: 35 Thanked 206 Times in 115 Posts Reputation: 216

Quote:
 Originally Posted by medpack87 A constant infusion of drug Y is begun. Drug Y has a Volume of Distribution of 5L, and a clearance of 0.05L/h. Aproximately how long would it take drug Y to reach steady state? a. 70 b. 100 c. 112 d. 280 e. 400
t1/2 = 0.7 X Vd / Cl

= 0.7 X 5 / 0.05

= 70.

 The above post was thanked by: neha_subh (04-02-2013)

#4
03-27-2013
 USMLE Forums Scout Steps History: Step 1 Only Posts: 57 Threads: 0 Thanked 60 Times in 22 Posts

You forgot it takes 4 t1/2 to get to steady state, Dr. Ali.

Quote:
 Originally Posted by Doctor Ali t1/2 = 0.7 X Vd / Cl = 0.7 X 5 / 0.05 = 70. Answer is A.
#5
03-27-2013
 USMLE Forums Newbie Steps History: Not yet Posts: 6 Threads: 0 Thanked 1 Time in 1 Post Reputation: 11

@q to all members
where to study pharmacokinetics n dynamics from?
#6
03-27-2013
 USMLE Forums Addict Steps History: Not yet Posts: 125 Threads: 17 Thanked 67 Times in 38 Posts Reputation: 77

Quote:
 Originally Posted by neesh @q to all members where to study pharmacokinetics n dynamics from?
kaplan+fa+uw
#7
03-28-2013
 USMLE Forums Veteran Steps History: Step 1 Only Posts: 283 Threads: 35 Thanked 206 Times in 115 Posts Reputation: 216

Truth is I got this question word to word including the numbers from the qbank. I picked 70 hrs X 4 = 280 hrs, and I got wrong. The correct answer was 70 hrs alone. I re-read the question and from there I came to know that all they wanted was half life alone; which in this case is 70 hours.
 The above post was thanked by: neha_subh (04-02-2013)
#8
03-28-2013
 USMLE Forums Addict Steps History: Not yet Posts: 117 Threads: 5 Thanked 59 Times in 40 Posts Reputation: 69

 The above post was thanked by: neha_subh (03-29-2013)
#9
03-29-2013
 USMLE Forums Veteran Steps History: 1 + CS Posts: 209 Threads: 18 Thanked 112 Times in 75 Posts Reputation: 122

A constant infusion of drug Y is begun. Drug Y has a Volume of Distribution of 5L, and a clearance of 0.05L/h.

Aproximately how long would it take drug Y to reach steady state?

d. 280

t 1/2 = 0.7 x Vd / CL

t 1/2 = 0.7 x 5 / 0.05

t 1/2=3.5 / 0.05

t 1/2 = 70

clinical steady state = 4-5 x t 1/2

so

clinical steady state = 4 X 70 = 280
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 The above post was thanked by: sami trailer (03-29-2013)
#10
03-31-2013
 USMLE Forums Guru Steps History: 1+CK+CS Posts: 316 Threads: 17 Thanked 159 Times in 97 Posts Reputation: 169

That question which I posted is a question from the Qmax question bank from FirstAid. The answer they give in their explanation is 70.

But I am also confused about this question, so I reported it, because it seems to me that they ask for steady state, and you need to multiply 70 x 4 to get 280 as most of you answered.

Also, in the explanation that comes with the question, they start by writing "First you need to calculate for half time", as if a second calculation would be needed to get to the answer, so even the explanation seems incomplete.

It is also known that FirstAid has some kinks, im 2 months away from the exam and im pretty sure the answer is 280, I hope I get a response from the FirstAid team.

 The above post was thanked by: neha_subh (04-02-2013)

 Tags Pharmacology-, Step-1-Questions

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