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#1
03-31-2011
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Calculated the half life for this drug?

A new antiepileptic drug is being studied. The first test subject is determined to have a volume of distribution of 60 L for this drug and a renal clearance of 4 L/hour. What is the approximate half life of this drug in this patient?

A - 2 hours
B - 7.5 hours
C - 10 hours
D - 15 hours
E - 18 hours

#2
03-31-2011
 USMLE Forums Guru Steps History: 1+CK+CS Posts: 390 Threads: 40 Thanked 365 Times in 144 Posts Reputation: 375

Cl = Vd x 0,67/half life
half life = Vd x 0.67/Cl = 60 x 0.67/4 = 10 hours

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 The above post was thanked by: aktorque (04-01-2011), Lena (06-26-2011), star123 (06-19-2011)
#3
03-31-2011
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B , 7.5 hrs
#4
03-31-2011
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Quote:
 Originally Posted by earthpole A new antiepileptic drug is being studied. The first test subject is determined to have a volume of distribution of 60 L for this drug and a renal clearance of 4 L/hour. What is the approximate half life of this drug in this patient? A - 2 hours B - 7.5 hours C - 10 hours D - 15 hours E - 18 hours
I think about 7,5 hours because 60/2=30 and half life--->30/4=7,5 H
#5
03-31-2011
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Quote:
 Originally Posted by honour I think about 7,5 hours because 60/2=30 and half life--->30/4=7,5 H

Hey, why do we need to divide the vd by 2?
#6
03-31-2011
 USMLE Forums Guru Steps History: 1+CK+CS Posts: 460 Threads: 100 Thanked 233 Times in 147 Posts Reputation: 243

C. 10 hours. The initial formula was correct.
T1/2 = 0.7 x Vd/Cl
There's no need to divide by 2 ?!?
#7
03-31-2011
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,357 Threads: 194 Thanked 3,259 Times in 881 Posts Reputation: 3269

First we know that:

k = 0.693 / t 1/2 ==> t 1/2 = 0.693 / k

and

Clearence = V * k ==> k = Clearence / V

then,

t 1/2 = ( 0.693 * V ) / Clearence ==> 0.693 * 60 / 4 = 10 aprox.

C - 10 hours
 The above post was thanked by: aktorque (04-01-2011)
#8
04-01-2011
 USMLE Forums Guru Steps History: Step 1 Only Posts: 487 Threads: 95 Thanked 1,458 Times in 356 Posts Reputation: 1468

Quote:
 Originally Posted by bebix First we know that: k = 0.693 / t 1/2 ==> t 1/2 = 0.693 / k and Clearence = V * k ==> k = Clearence / V then, t 1/2 = ( 0.693 * V ) / Clearence ==> 0.693 * 60 / 4 = 10 aprox. C - 10 hours
Quote:
 Originally Posted by harlesmd Cl = Vd x 0,67/half life half life = Vd x 0.67/Cl = 60 x 0.67/4 = 10 hours The answer is : C
Both of you are correct. Know the formula. You'll get easy calculation on the exam... easy points guys... know the formula.
 The above post was thanked by: bronchiole (04-02-2011), harlesmd (04-01-2011)

 Tags Pharmacology-, Step-1-Questions

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