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Old 02-14-2011
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Drug steady-state concentration

Drug Y has a volume of distribution (Vd) of 75 L in both younger and older adult men. In younger adults, it has a clearance rate of 15L/h, 50% of which is via the liver and 50% via the kidneys. For younger men, the maintenance regimen is 100 mg every 6 hours. Which of the following regimens will produce essentially the same steady-state concentration in an older man, whose creatinine clearance is half that of younger men, but whose hepatic function is unimpaired?


A. 75 mg every 3 hours
B. 75 mg every 6 hours
C. 75 mg every 9 hours
D. 100 mg every 3 hours
E. 100 mg every 6 hours
F. 100 mg every 12 hours
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Old 02-14-2011
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correct answer is B.....


note :

maintainance dose = clearance X steady state conc. X dosing interval


so if clearance is reduced to half (in older ppl) then maintainance dose shud be reduced to half (provided that dosing interval is constant) to reach the same steady state conc.


note here only 50% of drug is excreted by kidney, so dose reduction shud be of only renally excreted drug that is 50mg , now resdution of 50 to half 25+50(excreted by liver) = 75 mg.....



so 75 mg after every 6 hours
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Quote:
Originally Posted by shaan.medico View Post
correct answer is B.....


note :

maintainance dose = clearance X steady state conc. X dosing interval


so if clearance is reduced to half (in older ppl) then maintainance dose shud be reduced to half (provided that dosing interval is constant) to reach the same steady state conc.


note here only 50% of drug is excreted by kidney, so dose reduction shud be of only renally excreted drug that is 50mg , now resdution of 50 to half 25+50(excreted by liver) = 75 mg.....



so 75 mg after every 6 hours
Very good... I like your explanation.
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Old 02-14-2011
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Im not really a math person, I absoleutly hate it.. I hated all the equations and stuff uptill now (biostats, pharm & patho mostly - yet to do physio)

So I was wondering.. what is the prevalence of mathematical type questions? I suck at it, and tbh will screw up no matter how well prepared I am for them
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Old 02-14-2011
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Even without the equation, one can figure it out. See of 100mg, 50mg cleared by liver, 50 by kidneys (25 by each). So with removal of one kidney, subtract 25, we are left with 75 mg in 6 hours.
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Originally Posted by doctorsmonsters View Post
Even without the equation, one can figure it out. See of 100mg, 50mg cleared by liver, 50 by kidneys (25 by each). So with removal of one kidney, subtract 25, we are left with 75 mg in 6 hours.
Well, not only this question.

I meant other question in general that DO require equations etc.
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Old 02-14-2011
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haha, of course! and it wasn't in response to your post, I am pretty bad at all the equations and stuff myself, so when I saw the question, I tried to solve it without going through the pain of trying to recall the equation.
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Originally Posted by doctorsmonsters View Post
haha, of course! and it wasn't in response to your post, I am pretty bad at all the equations and stuff myself, so when I saw the question, I tried to solve it without going through the pain of trying to recall the equation.

Im not really a math person, I absoleutly hate it.. I hated all the equations and stuff uptill now (biostats, pharm & patho mostly - yet to do physio)

So I was wondering.. what is the prevalence of mathematical type questions? I suck at it, and tbh will screw up no matter how well prepared I am for them
That's right, it's not all about solving an equation and doing numbers. It's all about understanding the concept. I did so many physio and biostat qns by using the concepts. But I recommend you to do some practice qns on that particular subjects so you will not panic on the exam....
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wats the correct ans i gess its c 75mg in 9hrs
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Originally Posted by medico.in View Post
wats the correct ans i gess its c 75mg in 9hrs
No!!! it's B) 75 mg every 6 hours
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