# 0.2% of 50ml/ml preperation

1. Aug 31, 2011

### riezer

Hi,

Supposed you have a 500mg powder in a vial and you want to prepare a solution containing 0.2% solution. Supposed the vial can only be put 10ml.. giving a concentration of 50mg/ml in the vial or 5% solution. How do you create 0.2% out of this? Thanks.

2. Aug 31, 2011

### riezer

btw.. the 0.2% solution must be put in a bottle that is 8ml. Thanks..

3. Sep 1, 2011

### Staff: Mentor

Please elaborate, your description is so vague it is not clear what you can and what you can't do. And why the restrictions?

4. Sep 1, 2011

### riezer

Ok. A pharmacy wants to mix 0.2% Vancomycin for eye drop. It has a 500 mg powder vancomycin in a vial. It injects a 10 ml saline water into the vial. This makes the concentration in the vial
500mg/10 ml or 50mg/ml or 5% solution. Now to make it 0.2% solution. I wonder what is the procedure to do it. I'm just curious how they mix dilutions and stuff. Any idea how to get 0.2% out of it. Think of this as an exercise in math and chemistry. Of course we won't mix it and give it to people. I'm just curious how they did it. Thanks.

5. Sep 1, 2011

### riezer

btw... the 8ml is because the vancomycin eye solution is put in an empty 8ml container and 0.2% solution. Don't worry. I won't actually do it and give it to people. I just want to know how the diluioins and calculations is done.

6. Sep 1, 2011

### riezer

btw.. I know what they did is draw a few ml from the vial containing the 500mg/10ml or 50mg/ml or 5% and mix it with more parts of saline liquid into the 8ml vial to make it 0.2%. Now what must be the concentration of concentrated liquid taken from vial and taken from saline liquid?

7. Sep 2, 2011

### Staff: Mentor

Use definition of percentage concentration to find out what should be the mass of the solution so that 500mg makes 0.2% of it, assume saline liquid density to be 1g/mL.

I am moving the thread to homework section, even if it is not HW, it is clearly HW like type question.

8. Sep 2, 2011

### riezer

From a book. I found out here's what they did to make the concentration 2.5% from 5.0%. First after putting 10ml to 500mg to create 50mg/ml. They draw 5 ml from this and then add 5 ml saline liquid which makes the concentration half or 2.5%. Now if you add 10ml to it (the other 10ml).. the concentration will be half to 1.25%. But the total volume is 20ml. So I wonder if there is some formula where one can create 0.2% to fit 8ml. Anyone?

9. Sep 2, 2011

### Staff: Mentor

I already told you how to calculate dilution.

You can't prepare 8mL of 0.2% solution using all 500mg of the sample, you have to throw away part of it. That means - for example - preparing larger volume of 0.2% solution, and taking just 8mL.

10. Sep 2, 2011

### jmarsiglio

what does 0.2% mean? How many grams per how many ml?

and 5%, how many grams per same amount of ml?

Think about how you can dilute the 5% in order to make it same ratio as 0.2%. If the ratio of 0.2% is for example 1:5 and the other is 1:2 (they aren't), then you would 3 more ml for each gram. Then multiply this ratio until you have the number of grams originally in the vial. So if you want 500mg, then 1g :2ml + 3ml, divide by 2 is 0.5g : 2.5ml.

This is what I think, but I'm just a student.

Last edited: Sep 2, 2011
11. Sep 2, 2011

### riezer

When you see any eye ointment or other drops. You can always see the concentration. 0.2% is 2mg/ml. 5% is 50mg/ml. To convert from mg/ml to percent.. simply move one decimal to the left.

To convert from percent to mg/ml. Simply move one decimal to the right. So 5% is 50mg/ml.

Now 0.2% is 2mg/ml. Without using the powder but just injecting initial 10ml to the 500mg vial. The challenge is how do you make 0.2% solution that is 8ml by mixing with salt liquid and of course not using the whole 10ml of the vial (Borek saying to discard it or leave it as it is).

Think about how you can dilute the 5% in order to make it same ratio as 0.2%. If the ratio of 0.2% is for example 1:5 and the other is 1:2 (they aren't), then you would 3 more ml for each gram. Then multiply this ratio until you have the number of grams originally in the vial. So if you want 500mg, then 1g :2ml + 3ml, divide by 2 is 0.5g : 2.5ml.

This is what I think, but I'm just a student.[/QUOTE]

12. Sep 2, 2011

### jmarsiglio

I could show you but I'm not sure if that's allowed.

13. Sep 3, 2011

### Staff: Mentor

It is not - see forum rules.

14. Sep 3, 2011

### riezer

Don't forget the question is not really for a homework.

15. Sep 4, 2011

### Staff: Mentor

Doesn't matter. We can't tell if it is HW or not (and you would be surprised to know how often people lie about it), so all such questions are treated exactly the same way.

16. Sep 5, 2011

### riezer

Of course this is not a homework. What kinds of homework ask for formula. Anyway. According to the book "Blepheritis and Conjunctivitis: Guidelines for Diagnosis and Treatment":

"Vancomycin

Add 10ml sterile water (without preservative) to 500mg of vancomycin dry powder to form a 5.0% solution of 50mg/ml. To prepare a 25mg/ml concentration (2.5%), take 5 ml of 50mg/ml solution and add 5 ml of sterile water."

Anyway. You guys are saying the above instruction doesn't really produce 2.5% concentration?

17. Sep 6, 2011

### Staff: Mentor

You would be surprised.

Close to 2.5%, but not exactly. Just plug and chug into the percentage definition. If you add 10 mL of water to 50 mg of substance, total mass is not 10 g, more like 10.5 g, so the concentration is not 5%, but

$$\frac {5 g}{10.5 g} * 100 \% = 4.76 \%$$

This error carries through the next step of the dilution.

In fact the value will be even different, as density of water is not exactly 1 g/mL, more like 0.99823 g/mL at 20 °C.

18. Sep 9, 2011

### riezer

I finally talked to the nurse who prepared the vancomycin solution. She said she put 10ml into the 500mg vancomycin power vial, then she draws 2ml and add 8ml distilled water to a small empty container. So since there is initial 50mg/ml in the original vial. 2ml equals 100mg so since she added 8ml and put this in an empty container.. then it's 100mg/8ml... which is equivalent to 12.5mg/ml or 1.25% solution (since 50mg/ml is equal to 5% solution). Right?

19. Sep 9, 2011

### Staff: Mentor

Which means 8 mL are either stored for later or thrown away.

No, it is not 100 mg/8mL. She adds 8 mL to 2 mL, so the final volume is not 8 mL.

20. Sep 9, 2011

### riezer

Yes, I have the remaining 8ml stored in a vial kept in ref in case we need to prepare more in the future.

Your LHC physics knowledge really comes handy. So it's 100mg/10mL or 10mg/ml or 1% solution, or 0.99998888% as you said earlier?

Maybe this is like a particle that can't be pushed to c in the LHC but close to c like 99.999888% the speed of light. Isn't it.