Powder Volume problem

by Curtis

The doctor orders Amoxicillin 165 mg/5ml. You only have Amoxicillin 250 mg/5 ml. When reconstituted with 60 ml of purified water, the total volume will be 100 ml of 250 mg/5 ml. How many milliliters need to be added to give a 165 mg/5 ml dose?

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Powder Volume problem

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Feb 13, 2012
The correct anwer
by: Anonymous

The correct answer is 112 ml

Sep 28, 2011
so which answer is right...?
by: ashley

so which answer is right...?

Aug 06, 2011
It's not clear.
by: Van

I do not know what you really asked. How many ml of 250mg/5ml add to 60ml water or how many ml of water add to 100ml of 250mg/5ml???

Jul 15, 2011
by: Anonymous

You can simplify this question by using C1V1=C2V2. (165mg/5ml)x=(250mg/5ml)100ml which gives X=151.5ml

Apr 16, 2011
Amoxil 165/5mL
by: Barb

This is how I would do this problem.
If the bottle is reconstituted according to the instructions then you will have a total of 5000mg/100mL in the bottle. No matter how much water you add you will still have 5000mg of drug in the bottle.
I would then set it like this 165/5 = 5000/X
X = 151.5mL
If you already have 100mL in the bottle will need to add another 51.5 mL to get 165mg/5mL
You can check it this way.
If you didn't change the volume the child would get 3.3mL which means that there are approximately 30 doses in the bottle. After you change the volume to 151.5mL there are still 30 doses in the bottle.

Apr 14, 2011
I'll give it a shot.
by: Keith

The question is a little vague, as far as saying what you have vs. what you want. So, let's try to work on it with the information you've been supplied.

Looks like the normal mixture yields:
100mL of 250mg / 5mL

What you want is:
To add extra water so it's 165mg / 5mL

You'll use basic algebra, but first you have to figure out what % strength you have and what you need. In which case you can just use proportions math. Like this:

what you have with the standard 60mL of water added. :

250mg - - - - X - -
---------- = -----------
5mL - - - -100mL

X = 5000mg = 5 Grams = 5%


what you WANT :

165mg - - - - X - -
---------- = -----------
5mL - - - -100mL

X = 3300mg = 3.3 Grams = 3.3%

SO, then you'll take what you know you can make, and then make it equal what you want. ( to find the difference )

The setup:

(.05) (100mL) = (.033) (100+X)

5 = 3.3 + .033X

1.7 = .033X

X = 51.52mL

BUT, don't forget to add back in the 60mL !

So the answer is 111.52mL

Apr 14, 2011
by: Anonymous

Could you please explain this questions,
I am also having some confusion about this problem.
This website is useful so much to me to prepare for the PTCB exam.


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