# 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

 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= 30g30 X .10 divided by .40 = 7.5grams

 Alligation Math by: Pharm Yes, you can also use an alligation:0% |___|30 parts---|10%|---40%|---|10 partsSo, 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 partExtra credit if you can do it in your head !

 Algebra by: J C1(V1) = C2(V2) Method1) Set-up equation.40(X) = .10 (30)2) Simplify .40(X) = 33) Isolate X3/.40 = 7.54. SolveX = 7.5

 Formula by: Anonymous Easy formula(desired/have) x (quantity) so (10/40)x30 = 7.5 Just remember d/h x q = answer