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Compounding pharmacy math

by KL

You have been asked to compound 30 g of a 10% w/w zinc oxide cream. You have a 40% w/w zinc oxide cream in stock. How much stock cream will you dilute with cream base to make the prescription?

Comments for Compounding pharmacy math

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solution
by: Anonymous

Is the answer 7.5 g?
Answer
by: cb

7.5 g of the 40% zinc oxide
Question
by: Anonymous

My answer was close to yours. Mine was just 7 instead of 7.5 and I would like for you to explain it to me please because I used the allegation chart and can't find my mistake.
7.5g
by: Anonymous

I used the c1v1=c2v2 equation. We want to make an ointment with the strength of 10% and 30g of it. We only have a 40% strength in stock however, to find how much we need to dilute.
C1= 40%
V1= (X)
C2= 10%
V2= 30g

30 X .10 divided by .40 = 7.5grams
Alligation Math
by: Pharm

Yes, you can also use an alligation:

0% |___|30 parts
---|10%|---
40%|---|10 parts

So, with this ratio, you could reduce it to 3 parts of 0% diluent and 1 part 40% active ingredient.

Now, take your final volume and figure out how much each part is:

30 Grams / 4 parts = 7.5 grams per part

Extra credit if you can do it in your head !
Algebra
by: J

C1(V1) = C2(V2) Method

1) Set-up equation

.40(X) = .10 (30)

2) Simplify

.40(X) = 3

3) Isolate X

3/.40 = 7.5

4. Solve

X = 7.5
Formula
by: Anonymous

Easy formula

(desired/have) x (quantity)
so (10/40)x30 = 7.5
Just remember d/h x q = answer

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