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#1
04-03-2012
 USMLE Forums Scout Steps History: Not yet Posts: 96 Threads: 15 Thanked 19 Times in 18 Posts Reputation: 29

At 6hr after IV administration of bolus dose, the plasma level of a drug is 5mg/L. If the vd=10L and the elimination half life=3h, what is dose administered.

a. 100mg
b. 150mg
c. 180mg
d. 200mg
e. 540mg

#2
04-03-2012
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,353 Threads: 94 Thanked 877 Times in 507 Posts Reputation: 890

d) 200

vd=ivdose/p concentration

10l=x/5
x=50

6h = 2 half lives.
200->100->50 -assuming that there is first order kinetics
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 The above post was thanked by: pradeeprox (04-04-2012)
#3
04-04-2012
 USMLE Forums Scout Steps History: Not yet Posts: 96 Threads: 15 Thanked 19 Times in 18 Posts Reputation: 29

this question is from kaplan pharma the questions after the chapter.
the answer given is A. i don't get it. maybe the answer the give is wrong ?

this is what they say ( i don't get it)

at 6ht after iv injection ( which corresponds to two half lives of the drug, the plasma level is 5mg/L . extrapolating back to zero time doubling plasma level for each half life results in initial plasma level at zero time ( CO) = 5x2x2mg/L=20mg/l

n thats not even an option lol I'm so lost.

#4
04-04-2012
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,684 Threads: 213 Thanked 1,600 Times in 660 Posts Reputation: 1610

Quote:
 Originally Posted by pathophysio1 extrapolating back to zero time doubling plasma level for each half life results in initial plasma level at zero time ( CO) = 5x2x2mg/L=20mg/l
They are saying that 20 mg/L is the initial plasma level at zero time.
So if you use DocSikorski's formula -

vd=ivdose/p concentration
IV Dose= Vd * Plasma Concenteration.
IV Dose = 10 L * 20 mg/L
IV Dose = 200 mg

So the answer is D) 200 mg.
 The above post was thanked by: Kabutar111 (04-09-2012)

 Tags Pharmacology-, Step-1-Questions

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