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  #1  
Old 11-21-2012
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Default half life question

oFor theophylline , Vd -35 L, CL -48 ml/min, t -8hs.
If IV infusion of theophylline is started at a rate of 48mg/min. How long it will take to reach 91.75% of Css?

o30 hrs
o15 hrs
o24 hrs
o16 hrs
o32 hrs
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Old 11-21-2012
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Default Another Q

#2:
A 65 yr old pt is being treated with amiodarone for chronic AF. He arrives in your clinic complaining of symptoms of hyperthyroidism. Lab analysis of blood sample indicates a plasma level of 6ug/ml, well above the the normal therapeutic range of 1.2 ug/ml. The half life of amiodarone is 25 days. If you discontinue his medication, how long you will need to wait for amiodarone's level to fall to 1ug/ml ?
o25 days
o50 days
o75 days
o82.5 days
o100 days
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Old 11-21-2012
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1..32hrs
2..75 days ?
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Old 11-21-2012
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1 - 30hrs
2 - 75 days.
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Old 11-21-2012
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1. 32 hrs
2. < 75 days but > 50 days.


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Old 11-21-2012
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I request some explanation for these answers plz.I am totally lost.Thanks

@KoolKiller88
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Quote:
Originally Posted by Doc4Step1 View Post
I request some explanation for these answers plz.I am totally lost.Thanks

@KoolKiller88
haha dude, Don't request. Just ask

ques1. theophylline half life is 8hrs
conc eliminated
50% in 1 half life
75% in 2 half life
87.5 (50%+25%+12.5%) in 3 half life
93.75% in 4 half life

So to get a steady state of 91.75% (which is approx of 93.75%)- 4 X half life = 4X8= 32hrs

2. Using above mentioned concept. to get 1ug/ml i.e. after eliminating 83.3% of plasma level.
= 3X half life= 3X25= 75.

Hope it helps
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Old 11-21-2012
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FA says 4half lives is 93.75% . The question given says 91%.

with 8hr per half life = 32 hrs.

i chose 30hr seeing that the question said 91%.
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Old 11-21-2012
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why is 32hr more correct that 30hr?
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Quote:
Originally Posted by mdsoon View Post
FA says 4half lives is 93.75% . The question given says 91%.

with 8hr per half life = 32 hrs.

i chose 30hr seeing that the question said 91%.
Ya true. 30 hrs more appropriate.
Didn't paid attention
1. A. 30 hrs
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Quote:
Originally Posted by koolkiller88 View Post
haha dude, Don't request. Just ask

ques1. theophylline half life is 8hrs
conc eliminated
50% in 1 half life
75% in 2 half life
87.5 (50%+25%+12.5%) in 3 half life
93.75% in 4 half life

So to get a steady state of 91.75% (which is approx of 93.75%)- 4 X half life = 4X8= 32hrs

2. Using above mentioned concept. to get 1ug/ml i.e. after eliminating 83.3% of plasma level.
= 3X half life= 3X25= 75.

Hope it helps
Thanks man.That helped a lot.
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  #12  
Old 11-22-2012
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#1: 32 (anything in the 90s you assume its 4 half lives)
#2: 75
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Old 11-22-2012
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Quote:
Originally Posted by SarahM View Post
#1: 32 (anything in the 90s you assume its 4 half lives)
#2: 75
first half life 50% of Css i.e 8hrs
second half life 75%of Css 16hrs
third half life 88% of Css 24 hrs
fourth half life 94%of Css 32 hrs

BUT question is asking about 91.75% of Css which should be between third and fourth half life so 30 hrs should be the answer but can you explain please how it is 32hrs????
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