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#1
04-12-2013
 USMLE Forums Newbie Steps History: --- Posts: 2 Threads: 1 Thanked 1 Time in 1 Post Reputation: 11

How long does it take drug X to get to steady state
(hours)? (Drug X has a half life of 6h, a Clearance of
5L/h and a rate of infusion of 10 mg/h )

1. 2
2. 3
3. 25
4. 30
5. 50

No idea how to answer this so if somebody could break it down step by step it would be much appreciated
 The above post was thanked by: zainsyed (05-01-2014)

#2
04-12-2013
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 824 Threads: 66 Thanked 465 Times in 298 Posts Reputation: 475

4-5 half lives are required to achieve steady state with constant drug infusion

4. 30 (5x6h)
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#3
04-12-2013
 USMLE Forums Veteran Steps History: 1 + CS Posts: 209 Threads: 18 Thanked 112 Times in 75 Posts Reputation: 122
corect answr is d) 30

clinical steady state = 4 to 5 t1/2 life
about 5 half life it wil take to reach the steady state so
5x6=30hrs.

with initial dose 10mg and constant infusion rate:

1st half life=5mg/hr
3rd half life= 8.8mg/hr
5th half life=9.5mg/hr
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Last edited by neha_subh; 04-12-2013 at 11:12 AM.

#4
04-12-2013
 USMLE Forums Newbie Steps History: --- Posts: 2 Threads: 1 Thanked 1 Time in 1 Post Reputation: 11

Thank you! Cant believe it was that easy!

 Tags Pharmacology-, Step-1-Questions

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