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#1
07-20-2011
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First Order Kinetics; How much of the drug will remain?

A patient was given a 160 mg of a drug IV and 80 mg was eliminated during the first 120 min. If the drug follows first order elimination kinetics how much of drug will remain 6 hours after its administration?
a. none
b. 10mg
c. 20 mg
d. 40mg
e. 60 mg
 The above post was thanked by: curiousmind (08-11-2012), Mashee (07-20-2011), pass7 (07-20-2011)

#2
07-20-2011
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c) 20 mg
#3
07-20-2011
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Quote:
 Originally Posted by yasirsattar75 A patient was given a 160 mg of a drug IV and 80 mg was eliminated during the first 120 min. If the drug follows first order elimination kinetics how much of drug will remain 6 hours after its administration? a. none b. 10mg c. 20 mg d. 40mg e. 60 mg
1 order kinetics
160 mg -> 80mg (50%) in 2h
t1/2 = 2h

then in 6 h = 3 t1/2
160 mg -> 80 mg -> 40 mg -> 20 mg
 The above post was thanked by: Mashee (07-20-2011), rulz (07-20-2011), star123 (07-21-2011), usluipek (07-20-2011)

#4
07-20-2011
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,684 Threads: 213 Thanked 1,590 Times in 660 Posts Reputation: 1600

Yup
Its 20 mg!

First order kinetics = a constant fraction of drug is eliminated over a period of time. (Basically, half life)

First 2 hrs = 160 to 80
Next 2 hrs = 80 to 40
Next 2 hrs = 40 to 20

After 6 hrs, there is 20 mg of drug left.
 The above post was thanked by: Mashee (07-20-2011), star123 (07-21-2011), usluipek (07-20-2011)
#5
07-21-2011
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c)20mg.In first order kinetics,fixed fraction of the drug is eliminated so after 6hrs it is 20mg

 Tags Pharmacology-, Step-1-Questions

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