Pharmacy calculations - working with powder volume

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Pharmacy calculations - working with powder volume

Postby TNIrisman » Mon May 14, 2007 10:18 am

Can someone please help me - I am a pharmacy student and I can't figure this stuff out.

What is a powder volume?

Example: You need to make an injectable solution with a final concentration of 375 mg/mL. On hand you have a vial that contains 1.5 grams with the instructions to add 3.3 mL. What is the powder volume?

Any help possible - I would be so greatful.

Posts: 1
Joined: Mon May 14, 2007 10:04 am

help with powder volume

Postby Guest » Mon Jul 16, 2007 4:08 am

What you need to do is convert your 1.5 G into milligrams first. Then you solve for x. You allready know your final concentration is to be 375 mg in 1 mL. Find out how many mL will be in your 1500 mg of drug. The answer is 4 mL. Your instructions are to add 3.3 mL of diluent. Subtract your total which is 4, from your 3.3 mL. the answer will be a powder volume of 0.7 mL. That is the displacement of the powder in the vial. Your vial will explode if you do not include a powder volume.

Re: Pharmacy calculations - working with powder volume

Postby CaitlanK » Thu Jul 28, 2011 4:05 am

The directions for mixing a 250mg/5ml liquid antibiotic state when 80ml of water are added to the contents of the bottle the resulting volume is 150ml. determine concentration of the drug in mg/5ml if only 40ml of water were added?

i already determined the total mg of the drug in the bottle which is 7500mg, i then determined the powder volume of the drug in the bottle which was 70ml. then i had to figure out the volume of the new product, which i solved by:
New Product(NP)=D+PV
NP= 110 ml
At the end of this problem i have to write out the new concentration as total mg drug in bottle/volume of new product
which would look like this 7500mg/110ml, in my textbook they converted that into 6.82mg/ml then converted that to 341mg/5ml.
My question is how did they get 7500mg/110ml to convert to 341mg/5ml.

Help im not understanding the conversion on the last question!

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