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#1
02-14-2011
 USMLE Forums Guru Steps History: Step 1 Only Posts: 487 Threads: 95 Thanked 1,458 Times in 356 Posts Reputation: 1468
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
 The above post was thanked by: Amenah (02-14-2011), ibukun (02-14-2011), Mahony87 (02-15-2011), Mondoshawan (02-14-2011), pnreddy (02-14-2011), shaan.medico (02-14-2011), zainsyed (05-01-2014)

#2
02-14-2011
 USMLE Forums Addict Steps History: 1 + CK Posts: 109 Threads: 26 Thanked 32 Times in 14 Posts Reputation: 42

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
 The above post was thanked by: aktorque (02-14-2011), Amenah (02-14-2011), ibukun (02-14-2011), kundra (02-14-2011), Mahony87 (02-15-2011), Mondoshawan (02-14-2011), prataptetali (02-15-2011)
#3
02-14-2011
 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 shaan.medico 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.
 The above post was thanked by: ibukun (02-14-2011), shaan.medico (02-14-2011)
#4
02-14-2011
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,175 Threads: 38 Thanked 852 Times in 478 Posts Reputation: 862

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
 The above post was thanked by: aktorque (02-15-2011), prepink (06-30-2011)
#5
02-14-2011
 USMLE Forums Guru Steps History: 1+CK+CS+3 Posts: 335 Threads: 24 Thanked 295 Times in 152 Posts Reputation: 305

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.
 The above post was thanked by: aktorque (02-15-2011), ibukun (02-14-2011)
#6
02-14-2011
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,175 Threads: 38 Thanked 852 Times in 478 Posts Reputation: 862

Quote:
 Originally Posted by doctorsmonsters 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.
 The above post was thanked by: aktorque (02-15-2011)
#7
02-14-2011
 USMLE Forums Guru Steps History: 1+CK+CS+3 Posts: 335 Threads: 24 Thanked 295 Times in 152 Posts Reputation: 305

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.
 The above post was thanked by: aktorque (02-15-2011)
#8
02-15-2011
 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 doctorsmonsters 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....
 The above post was thanked by: patelMD (02-15-2011), zainsyed (05-01-2014)
#9
02-15-2011
 USMLE Forums Scout Steps History: --- Posts: 62 Threads: 25 Thanked 11 Times in 8 Posts Reputation: 21
ans

wats the correct ans i gess its c 75mg in 9hrs
 The above post was thanked by: aktorque (02-15-2011)
#10
02-15-2011
 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 medico.in wats the correct ans i gess its c 75mg in 9hrs
No!!! it's B) 75 mg every 6 hours

 Tags Pharmacology-, Step-1-Questions

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