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certain
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A pharmacokinetics Question
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12.09.07 (12 months ago)
#1
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PLEASE HELP ME SOLVE THIS PROBLEM. I SAW IT IN A QUESTION BANK.i am very confused over this.
The clearance and volume of distribution of Amikacin in a a patient are 50ml/min and 20 L respectively. What dose should be administered every 8 hours to obtain a steady state plasma concentration of 20 mg/L.
THE ANS ARE
1.125mg
2.400mg
3.480mg
4.760mg
5.1000mg
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itsjusnobody
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12.09.07 (12 months ago)
#2
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im not sure but i'll try...
loading dose should be 400mg..
but your question's asking for maintenance of a steady state plasma conc...which is to say you will require a fixed quantity of the drug that will match elimination..
clearance= 50ml/min
required conc= 20mg/l which is same as 20mg/1000ml (since 1l=1000ml)
now, 1000ml contains 20mg
so, 50ml would contain- (50x20)/1000=1
therefore, 1mg of the drug is eliminated every minute therefore in 8 hrs= 1x60x8= 480mg of the drug would be eliminated.
so i think you should administer 480mg every 8hrs to attain a steady state conc.
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itsjusnobody
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12.09.07 (12 months ago)
#3
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if im wrong correct me..plz
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itsjusnobody
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12.09.07 (12 months ago)
#4
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also remember..amikacin's an aminoglycoside..so if ur gonna give it thru the oral route, there wont be any absorption, so its presumed in the question that ur givn it IV.
this makes ur calculation simpler by not considering bioavailability
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Siyaa
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12.10.07 (12 months ago)
#5
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Hi certain , did u try using the following equation
Miantenance dose= Clearance X Steady State Concentration X dosing interval
It comes out to be 480
what s answer with u in question bank?
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itsjusnobody
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12.10.07 (11 months ago)
#6
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you got that equation from kaplan's right?
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itsjusnobody
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12.10.07 (11 months ago)
#7
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but they never gave the derivation of all that list of equations, and so never understood them..
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Siyaa
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12.10.07 (11 months ago)
#8
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| Siyaa wrote: |
Hi certain , did u try using the following equation
Miantenance dose= Clearance X Steady State Concentration X dosing interval
It comes out to be 480
what s answer with u in question bank? |
This equation has
clearance x steady state concentration which means amount of drug being removed wrt a particular vol in a min .
and then multiplied by dosing interval shows total removed in that particular time .
It isnt given in splitted form in old text books too and as such u have indirectly done same thing, so it is fine.
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katy
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12.10.07 (11 months ago)
#9
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thanks syaa,itsjusnobody for explanation
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certain
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12.14.07 (11 months ago)
#10
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Hi
The answer is 480mg . Thanks a lot everyone for the derivation!
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