Alligation/Alternate Purpose: An easy method to make a new strength from two existing strengths

Sample Problem Triamcinolone cream is available in strengths of 0.1% and 0.5%. What quantity of 0.1% and 0.5% cream is needed to make 100 grams of 0.2% triamcinolone cream?

Basic Set Up % strength starting Material #1 % strength starting Material #2 % strength desired (final product) % strength starting material #1 minus % strength desired (absolute value) % strength starting material #2 minus % strength desired (absolute value)

% strength starting material #2 minus % strength desired (absolute value) % strength starting material #1 minus % strength desired (absolute value) Value is the # of parts needed of starting material #1 Value is the # of parts needed of starting material #2 Total # of parts needed

Value is the # of parts needed of starting material #2 Value is the # of parts needed of starting material #1 Total # of parts needed Ratio needed for starting material #1 Ratio needed for starting material #

Ratio needed for starting material #1 Ratio needed for starting material #2 Final amount of product desired Amount needed of starting material #1 Amount needed of starting material # grams 75 grams 0.1% cream 25 grams 0.5% cream

Answer 75 grams 0.1% cream 25 grams 0.5% cream 100 grams 0.2% cream

Example Problem How much of a 20% hydrocortisone (HC) cream and how much of a 5% HC cream would be needed to make 50 grams of a 9% HC cream?

Basic Set Up 20% 5% 9% 11 parts 4 parts

11 parts 4 parts 11 parts 15 parts

11 parts 4 parts15 parts

50 grams 13.3 grams 36.7 grams grams

36.7 grams of 5% HC cream 13.3 grams of 20% HC cream 50 grams of 9% HC cream

Created by: Jeff Sundell & Doug White