Pharmacy IV Math Question: Weight/Volume Dextrose in Water to Add to 500cc D10W

by Don
(Seattle)

IV Dextrose in Water-Weight/Volume Pharmacy Math Question

IV Dextrose in Water-Weight/Volume Pharmacy Math Question

A pharmacist needs to compound an IV which is 8% w/v dextrose in water. How many cc of pure sterile water should she add to 500cc of D10W to make the IV?

I would appreciate the help!

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starstarstarstarstar 		Dilution / Compounding Pharmacy Math Question...
by: David

To start with, D10W is 10% Dextrose in Sterile Water. We have 500cc or MLs of this hydration.

What we are trying to make or compound is 8% Dextrose in Sterile Water.

This is a dilution math problem.

Keep in mind, 10% Dextrose in 500ML of Sterile water is percent weight in volume (w/v). This means that weight (in this question, 10 grams (w/v is figured per 100ML of liquid) in volume = 50gms/500ML = 10%.

What we want to get to is 8% weight in volume. How much sterile water do we need to add (volume) to get to this 8%?

8% is what decimal? 0.125

10% (50gm in 500ML)

50gm 50gm
---- = ---------------- = 8% = 0.125
500ML+R H = (500ML + R)

Where "R" is the sterile water volume to add and "H" is the final volume.

We want to dilute this solution 2%, from 10% to 8%.

So we plug these values into the equation:

50gm
----------------------------------
500ML + 125ML = 625ML

How does this convert into a percentage?

625ML X 0.08 (8%) = 50gm

8% = 625ML times 0.125 = 50gms

You (or your pharmacist) will need to add 125ML of Sterile water to the 500ML of D10W, making a total volume of 625ML. 8% of 625ML = 50GM.

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