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 03-30-2009, 02:05 PM #1 New Member   Status Pre-Pharmacy Join Date: Mar 2009 Posts: 1 Pharmaceutical Calcultion SDN Members don't see this ad. (About Ads) What is the final concentration of a sodium chloride solution obtained by mixing 100ml of 0.9% w/v with 200 ml of 0.45%w/v and 300ml of 0.2% w/v. Any help pls?
 03-30-2009, 02:22 PM #2 1K Member     Status: Pharmacist Join Date: Aug 2007 Posts: 1,979 good lord, this is really simple, just set up an equation. 100ml x 0.9% + 200ml x 0.45% + 300ml x 0.2% = 600ml x (X%) Solve for X%.
03-30-2009, 02:57 PM   #3
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Quote:
 Originally Posted by xiphoid2010 good lord, this is really simple, just set up an equation. 100ml x 0.9% + 200ml x 0.45% + 300ml x 0.2% = 600ml x (X%) Solve for X%.
What kind of equation is that?
(100x.9)+(200x.45)+(300x.2)=600ml????????????????? ??

03-30-2009, 03:33 PM   #4
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Quote:
 Originally Posted by Jaguis What is the final concentration of a sodium chloride solution obtained by mixing 100ml of 0.9% w/v with 200 ml of 0.45%w/v and 300ml of 0.2% w/v. Any help pls?
Figure out the mass of each drug contained in each individual solution, masses are neither created nor destroyed. Add all those masses together, you now have a total amount of drug in the final mixture. Add all the volumes together. although on a technicality depending on the solvent or base liquid it may not be exactly 600 mls but since we are dealing with only water as a base liquid its 600 mls.

one thing to note, its good to think about the amount of drug in a volume as opposed to a concentration because lets just say you take 10 mls out of the 0.9% solution into the syringe to mix it with another. The concentration is the same in the syringe, but the amount of the drug is different, and the amount of drug in the syringe will change the concentration in the new solution
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03-30-2009, 03:44 PM   #5
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Quote:
 Originally Posted by Quiksilver Figure out the mass of each drug contained in each individual solution, masses are neither created nor destroyed. Add all those masses together, you now have a total amount of drug in the final mixture. Add all the volumes together. although on a technicality depending on the solvent or base liquid it may not be exactly 600 mls but since we are dealing with only water as a base liquid its 600 mls. one thing to note, its good to think about the amount of drug in a volume as opposed to a concentration because lets just say you take 10 mls out of the 0.9% solution into the syringe to mix it with another. The concentration is the same in the syringe, but the amount of the drug is different, and the amount of drug in the syringe will change the concentration in the new solution
good call

03-30-2009, 03:49 PM   #6
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Quote:
 Originally Posted by Jaguis What is the final concentration of a sodium chloride solution obtained by mixing 100ml of 0.9% w/v with 200 ml of 0.45%w/v and 300ml of 0.2% w/v. Any help pls?
0.4%

03-30-2009, 04:38 PM   #7
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Quote:
 Originally Posted by Old Timer What kind of equation is that? (100x.9)+(200x.45)+(300x.2)=600ml????????????????? ??
what's wrong? I always set up equations exactly as how the question logically flows. In this case, you got 3 solutions of different concentrations, which will give you 600 ml of what concentration? And you are solving for that "what". Basic understanding of mass and volume is assumed.

03-30-2009, 08:15 PM   #8
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Quote:
 Originally Posted by xiphoid2010 what's wrong? I always set up equations exactly as how the question logically flows. In this case, you got 3 solutions of different concentrations, which will give you 600 ml of what concentration? And you are solving for that "what". Basic understanding of mass and volume is assumed.
Please send me a picture so if I see you behind the counter I can run the other way.

The way Quiksilverr described the process is the correct way to perform the calculation.

100ml x 0.9% + 200ml x 0.45% + 300ml x 0.2% = 600ml x (X%)

.9+.9+.6=600 x (x%) makes no sense and does not compute......

03-30-2009, 08:21 PM   #9
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Quote:
 Originally Posted by ItsOverZyvox 0.4%
Are you sure?

03-30-2009, 08:27 PM   #10
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Quote:
 Originally Posted by Old Timer Are you sure?

yeah.. I am.

03-30-2009, 08:29 PM   #11
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Quote:
 Originally Posted by Old Timer 100ml x 0.9% + 200ml x 0.45% + 300ml x 0.2% = 600ml x (X%)
That is correct.

03-30-2009, 08:38 PM   #12
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Quote:
 Originally Posted by Old Timer Please send me a picture so if I see you behind the counter I can run the other way. The way Quiksilverr described the process is the correct way to perform the calculation. 100ml x 0.9% + 200ml x 0.45% + 300ml x 0.2% = 600ml x (X%) .9+.9+.6=600 x (x%) makes no sense and does not compute......
looks like an old timer has gotten a little too old. My equation is correct.

03-30-2009, 09:39 PM   #13
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Quote:
 Originally Posted by xiphoid2010 looks like an old timer has gotten a little too old. My equation is correct.
Show me the math.

Quote:
 Originally Posted by ItsOverZyvox yeah.. I am.
So how many gms of NaCl are there in 600 ml?

 03-30-2009, 09:48 PM #14 P2 Wildcat   Status: Pharmacy Student Join Date: Jul 2007 Location: Tucson, AZ Posts: 1,484 Both ways come out exactly the same. Yeah, I'm so geeky for actually having done that but I didn't understand why xiphoid's equation wouldn't work.
03-30-2009, 10:03 PM   #15
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Quote:
 Originally Posted by xiphoid2010 good lord, this is really simple, just set up an equation. 100ml x 0.9% + 200ml x 0.45% + 300ml x 0.2% = 600ml x (X%) Solve for X%.
This is how I was taught to solve these problems: just add up the individual components and come out with a total mixture. It's probably the most logical way of doing it.

03-30-2009, 10:09 PM   #16
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Quote:
 Originally Posted by Old Timer Show me the math. So how many gms of NaCl are there in 600 ml?
.004 x 600 = 2.4 grams

xiphoid's approach isn't excessive, excessive is how I used to approach questions where you have various concentrations and have to solve for quanities of each to produce a fixed volume of certain concentration.

I used to approach these using systems of equations before a teacher pointed out using alligation to save me the time.

03-31-2009, 04:37 AM   #17
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Quote:
 Originally Posted by Old Timer Show me the math.
Which part of my simple equation don't you understand? It's really just simple logic equation of "total is the sum of all of its individual components", as confirmed by all the others in this forum.

03-31-2009, 04:44 AM   #18
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Quote:
 Originally Posted by powertoold This is how I was taught to solve these problems: just add up the individual components and come out with a total mixture. It's probably the most logical way of doing it.
yeah, thanks. My equation is a simple summation of all the components to solve for a single variable, and I thought it's very self explanatory.

Does anyone understand why Old Timer is not understanding my equation? Is it that hard to understand?

03-31-2009, 05:42 AM   #19
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Quote:
 Originally Posted by xiphoid2010 yeah, thanks. My equation is a simple summation of all the components to solve for a single variable, and I thought it's very self explanatory. Does anyone understand why Old Timer is not understanding my equation? Is it that hard to understand?
Sure, when you make a calculation like this, it is safer to show your work and break down each component of the problem. If you were my student and you had to make a compound I would not let you do what you dud because it is faster or easier. The way Quicksilver described solving it is the only safe way. I know I'm being a pain in the a**, but I have seen to many errors over the years using the method you have described. It's so easy to end up off by a factor of 10 or a factor of 100. I had a student just this past week, do what you did and they used your formula and they were off by a factor of 10....

That's why I said show me the math..... Only It's Over gave the answer, just without any math so I asked if he was sure.

03-31-2009, 07:33 AM   #20
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Quote:
 Originally Posted by xiphoid2010 yeah, thanks. My equation is a simple summation of all the components to solve for a single variable, and I thought it's very self explanatory. Does anyone understand why Old Timer is not understanding my equation? Is it that hard to understand?
Its not all that simple to understand. Yeah, its a one step problem but to understand what is conceptually going on, it is easier with my method. When you have a first time learner, the only way they are going to learn it is to conceptualize it. just my 2 cents

03-31-2009, 09:18 AM   #21
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Quote:
 Originally Posted by Quiksilver Its not all that simple to understand. Yeah, its a one step problem but to understand what is conceptually going on, it is easier with my method. When you have a first time learner, the only way they are going to learn it is to conceptualize it. just my 2 cents
Hmmm, maybe it's an asian thing. Math has always been like a natural language to me and very easy to understand and work with. Then again, maybe it's the difference in how little and much emphasis US and asian education system put on math.

03-31-2009, 09:26 AM   #22
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Quote:
 Originally Posted by Old Timer Sure, when you make a calculation like this, it is safer to show your work and break down each component of the problem. If you were my student and you had to make a compound I would not let you do what you dud because it is faster or easier. The way Quicksilver described solving it is the only safe way. I know I'm being a pain in the a**, but I have seen to many errors over the years using the method you have described. It's so easy to end up off by a factor of 10 or a factor of 100. I had a student just this past week, do what you did and they used your formula and they were off by a factor of 10.... That's why I said show me the math..... Only It's Over gave the answer, just without any math so I asked if he was sure.
Different people work the thought process differently. Students should use whatever thought process that works best and accurate for them, as long as the result is correct. I'll be more prone to error and not as efficient if I had to change my thought process into ones that's some one else's. My process worked best for me since I came out among the top of my class in both Pharm Calc and PK, and arrived at the answers faster than most.

03-31-2009, 01:15 PM   #23
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Quote:
 Originally Posted by xiphoid2010 Hmmm, maybe it's an asian thing. Math has always been like a natural language to me and very easy to understand and work with. Then again, maybe it's the difference in how little and much emphasis US and asian education system put on math.
but lack the skills to communicate that across....

Touche my friend.

03-31-2009, 01:22 PM   #24
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Quote:
 Originally Posted by Quiksilver but lack the skills to communicate that across.... Touche my friend.
Math is the universal language. Learn it, speak it.

But agreed, asian education system focus way more on math and sciences. I was raised on that formula, at the expense of being more "well rounded". While I'm sure I will suck as a politician or a salesman, but let's just say no love lost there.

Last edited by xiphoid2010; 03-31-2009 at 01:27 PM.

03-31-2009, 01:47 PM   #25
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Quote:
 Originally Posted by xiphoid2010 Different people work the thought process differently. Students should use whatever thought process that works best and accurate for them, as long as the result is correct. I'll be more prone to error and not as efficient if I had to change my thought process into ones that's some one else's. My process worked best for me since I came out among the top of my class in both Pharm Calc and PK, and arrived at the answers faster than most.

Oh yeah? What's the extrapolated Cmax for Tobramycin 7mg/kg dose?

quick.

 03-31-2009, 01:50 PM #26 Retired   Join Date: Jul 2008 Posts: 2,282 3 minutes elapsed.
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03-31-2009, 01:56 PM   #28
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Quote:
 Originally Posted by ItsOverZyvox Oh yeah? What's the extrapolated Cmax for Tobramycin 7mg/kg dose? quick.
no tobra dosing was taught. What's Tobra's Vd, infusion time, infusion method, number of doses given, how is it cleared? LOL

 03-31-2009, 01:59 PM #29 1K Member     Status: Pharmacist Join Date: Aug 2007 Posts: 1,979 what you don't know those parameters off the top of your head? Shame on you zyvox. 3 minutes. :P
 03-31-2009, 02:00 PM #30 Retired   Join Date: Jul 2008 Posts: 2,282 I'm a little disappointed.. you tell me what the VD is I'll tell you the infusion time is 60 minutes. You tell me how it's cleared and I'll tell you that only 1 dose is given. Infusion method???????? You tell me.
03-31-2009, 02:01 PM   #31
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Quote:
 Originally Posted by xiphoid2010 what you don't know those parameters off the top of your head? Shame on you zyvox. 3 minutes. :P

I was out cracking and eating walnuts. I'm off to the range. I expect answers when I get back.

03-31-2009, 02:07 PM   #32
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Quote:
 Originally Posted by ItsOverZyvox I'm a little disappointed.. you tell me what the VD is I'll tell you the infusion time is 60 minutes. You tell me how it's cleared and I'll tell you that only 1 dose is given. Infusion method???????? You tell me.
Sorry, I'm not doing the looking up for you since you are not paying me to work for you. You want answers, you need to give me all the relevant parameters. And there are a lot of parameters. You are start off by looking up if it's one compartment model or 2. Mean while I gota go to my Business Management elective. See you when I come back, have fun researching.

 03-31-2009, 02:13 PM #33 Retired   Join Date: Jul 2008 Posts: 2,282 I already know the answer with the parameters given. Just wanted to see how fast you can calculate it because you bragged about your pk and math prowess.
03-31-2009, 03:32 PM   #34
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Quote:
 Originally Posted by ItsOverZyvox Oh yeah? What's the extrapolated Cmax for Tobramycin 7mg/kg dose? quick.
Don't you either need a peak or trough or better yet patient parameters in order to solve this gem. I mean all i know is the long way to the answer.

also don't you need to know dosing interval and infusion time?

PS I'm not so bad at PK myself, and im not asian

Last edited by Quiksilver; 03-31-2009 at 03:42 PM. Reason: also don't you need to know dosing interval and infusion time?

03-31-2009, 03:37 PM   #35
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Quote:
 Originally Posted by Quiksilver Don't you either need a peak or trough or better yet patient parameters in order to solve this gem. I mean all i know is the long way to the answer.
no.

03-31-2009, 03:52 PM   #36
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Quote:
 Originally Posted by ItsOverZyvox no.
are you going to leave me hanging? do you assume values of some of the variables?

 03-31-2009, 03:55 PM #37 Retired   Join Date: Jul 2008 Posts: 2,282 I asked for extrapolated Cmax. What's the formula for Cmax?
 03-31-2009, 03:56 PM #38 Member     Status: Pharmacist Join Date: Mar 2009 Location: Los Angeles Posts: 64 Cmax = too high EDIT: for traditional dosing! Last edited by codep1nk; 05-27-2012 at 09:55 AM. Reason: temporary insanity
03-31-2009, 03:56 PM   #39
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Quote:
 Originally Posted by xiphoid2010 Sorry, I'm not doing the looking up for you since you are not paying me to work for you. You want answers, you need to give me all the relevant parameters. And there are a lot of parameters. You are start off by looking up if it's one compartment model or 2. Mean while I gota go to my Business Management elective. See you when I come back, have fun researching.
its multiple compartment system. However you trap your calculations within a certain time window and you don't worry about number of compartments because you are only dealing with a single compartment.

03-31-2009, 03:57 PM   #40
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Quote:
 Originally Posted by Quiksilver its multiple compartment system. However you trap your calculations within a certain time window and you don't worry about number of compartments because you are only dealing with a single compartment.
that is true.

03-31-2009, 03:58 PM   #41
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Quote:
 Originally Posted by codep1nk Cmax = too high Even for extended interval...or even daily dose of a CF kid..

What's too high? What's the optimum bacteriocidal concentration of aminoglycoside against pseudomonas?

03-31-2009, 04:00 PM   #42
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Quote:
 Originally Posted by ItsOverZyvox What's too high? What's the optimum bacteriocidal concentration of aminoglycoside against pseudomonas?
edited post =]
not too high for CF kid's daily dosing

pseudomonas where?

03-31-2009, 04:03 PM   #43
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Quote:
 Originally Posted by codep1nk edited post =] not too high for CF kid's daily dosing pseudomonas where?

Location of pseudomonas would be irrelevant as far as determining the optimum bacteriocidal concentration. Location of infection on the other hand is important in determining the dose to attain certain peak.

03-31-2009, 04:04 PM   #44
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Quote:
 Originally Posted by ItsOverZyvox Location of pseudomonas would be irrelevant as far as determining the optimum bacteriocidal concentration. Location of infection on the other hand is important in determining the dose to attain certain peak.
Hah, that's what i meant...psa INFECTION where?

 03-31-2009, 04:05 PM #45 *     Status: Pharmacist Join Date: Mar 2009 Posts: 296 You (royal) are really overdoing this. I'm grateful I had a applied kinetics rotation. We could start a patient on vancomycin with just weight and SCr. I'll be darned if those levels didn't come back correct to the tenth decimal place on a few occasions. Of course we'd refine the dose after viewing the levels, but population parameters were remarkably effective.
 03-31-2009, 04:05 PM #46 Retired   Join Date: Jul 2008 Posts: 2,282 Dang, what good is all the PK education that's so convoluted with concepts and formulas that you guys can't see a clear cut day to day practical application of how to dose ?
03-31-2009, 04:06 PM   #47
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Quote:
 Originally Posted by rphello You (royal) are really overdoing this. I'm grateful I had a applied kinetics rotation. We could start a patient on vancomycin with just weight and SCr. I'll be darned if those levels didn't come back correct to the tenth decimal place on a few occasions. Of course we'd refine the dose after viewing the levels, but population parameters were remarkably effective.

Thank you.

03-31-2009, 04:06 PM   #48
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Quote:
 Originally Posted by ItsOverZyvox I asked for extrapolated Cmax. What's the formula for Cmax?
Cpeak = [Dose/CL*T(infusion time)*(1-e^-kT)*e^-kt2 (1/2 hr in this case)]/1-e^-kt (dosing interval)

I am missing a clearance.

03-31-2009, 04:07 PM   #49
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Quote:
 Originally Posted by rphello You (royal) are really overdoing this. I'm grateful I had a applied kinetics rotation. We could start a patient on vancomycin with just weight and SCr. I'll be darned if those levels didn't come back correct to the tenth decimal place on a few occasions. Of course we'd refine the dose after viewing the levels, but population parameters were remarkably effective.
who's royal?

03-31-2009, 04:09 PM   #50
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Quote:
 Originally Posted by Quiksilver Cpeak = [Dose/CL*T(infusion time)*(1-e^-kT)*e^-kt2 (1/2 hr in this case)]/1-e^-kt (dosing interval) I am missing a clearance.
u can use a simpler estimate...
cmax = dose/vd

still dont have vd...but if we had a weight...you could estimate that as well with the population parameter...but no weight either.
b/c for traditional dosing, generally don't dose 7mg/kg of an aminoglyc unless its amikacin...

Last edited by codep1nk; 05-27-2012 at 09:56 AM. Reason: typo

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