A pharmacist receives a prescription for 60 g of a 0.75% w/w bexarotene gel. How many grams each of a 1% w/w bexarotene gel and gel base must be used?

Question

Using this: Altering Strength, Stock Solutions, and Alligation Calculations

Answer 1

60 g x 0.75 g / 100 g = 0.45 g of bexarotene is needed

1% bexarotene gel = 1 g bexarotene / 100 g gel

To get 0.45 g from this prep, you need...

0.45 g bex x 100 g gel / 0.01 g bex = 45 g gel

That leaves 15 g of gel base

Summary:

take 45 g of 1% bexarotene gel and mix with 15 g of gel base to get 60 g of 0.75% bexarotene

Alligation

Have...........Need..........Parts

1%...................................0.75

...................0.75.................

0%...................................0.25

To make 60 g (1 part), take 0.75 parts of 1% and mix with 0.25 parts of 0%(gel base)

Converting parts to grams, we have 0.75 parts x 60 g = 45 grams of 1%

0.25 parts x 60 g = 15 g of 0% (gel base)

Mix 45 g of 1% bexarotene gel with 15 g of gel base