COMPOUNDING CALCULATIONSJessica Johnson, Pharm. D.

TOPICS• Percent Concentrations• Ratio Concentrations• Determining # of tabs/caps needed to reformulate into a

liquid• Recipes

• Enlarging• Reducing

PERCENT CONCENTRATIONS• Units need to ALWAYS be in grams and/or milliliters• w/v = weight/volume = grams/mL

• Used when a solid is mixed into a liquid

• v/v = volume/volume = mL/mL• Used when a liquid is mixed into another liquid

• w/w = weight/weight = grams/grams• Used when a solid is mixed into another solid

Example (w/w):• Ibuprofen 10% cream (w/w)• The w/w tells us that the ibuprofen is a solid, and we are

mixing it into another solid to obtain a 10% cream

• Thus, 10% can be written as follows:

• There are 10 grams of ibuprofen per 100 grams of cream

• If we were trying to determine how much ibuprofen is in 45 g of cream, we could then use a proportion:

• = • Our answer would be 4.5 grams Ibuprofen

Example (w/v):• Lisinopril 20% solution (w/v)• The (w/v) tells us that lisinopril is a solid, and we are

mixing it into a liquid to obtain either a solution or suspension

• The 20% can be written as follows:

• There are 20 g of Lisinopril per 100 mL of liquid

• If we wanted to know how many grams of lisinopril are needed to make 240 mL of the lisinopril liquid, we could use a proportion:

• = • There are 48 grams of lisinopril in 240 mL of the liquid

• Using the example from the previous page, say that we wanted to know how much liquid we could make from 15 grams of lisinopril. How would that be set up?

Practice – Percent Concentrations• You receive a prescription for a compound containing

1.5% hydrocortisone in Eucerin cream (w/w). If you need to dispense 140 grams, how much hydrocortisone should be used? How much Eucerin?

• First, determine how much hydrocortisone would be used by setting up a proportion• = • X = 2.1 grams hydrocortisone

• Second, take the final amount wanted (140 grams) and subtract the amount of hydrocortisone to determine how much Eucerin should be used • 140 grams – 2.1 grams = 137.9 grams Eucerin

Practice – Percent Concentrations• You need to make a Prevacid solution (w/v) that contains

3% Prevacid. If you are making a total of 35 mL of the solution, how many g of Prevacid should be used?

Practice – Percent Concentrations• You need to make Ranitidine 4% solution for a patient. If

you are making 5 ounces total, how many mg of ranitidine should be used?

• Hint: Watch your units!

Questions?

Ratio Concentrations• Same idea as percent concentrations, but using ratios

instead• The units are STILL grams and mL• Recall how a ratio would appear:

• 1:10,000 (w/v)

• In this case, we set up the proportion using the EXACT numbers from the ratio:

Example:• You have an epinephrine solution that is 1:5000 (w/v).

How many grams of epinephrine would be in 2 mL of soluion?

• Set up the proportion using the numbers from the ratio• =

• X = 0.0004 grams epinepherine

Ratio - Practice• You are making a solution (w/v) that is to contain 1:4000

active drug. If you are making a total of 100 mL, how many grams of active drug should be used?

Ratio Percent• In some cases, you may be asked to turn a ratio into a percent

• Example: What percentage is a solution (w/v) that has a concentration of 1:10,000?

• To do this, use a proportion starting with your ratio:

• = • X = 0.01%

• REMEMBER! When x/100, x is equal to a percentage! (Part per 100)

• When you use proportions, there is NO MOVING DECIMALS. IT IS ALREADY ACCOUNTED FOR.

Ratio Percent Practice• Convert the ratio 1:12,500 (w/v) to a percent.

Percent Ratio• You may also be asked to convert a percent to a ratio

• Again, we can set up a proportion:

• Convert 0.05% into a ratio• Question: What number do ratios ALWAYS start with?

• = • X = 2000• Ratio = 1:2000

Percent Ratio Practice • Convert 0.002% to a ratio

Questions?

Determining the # of tablets to use for a compound• Sometimes, pharmacists and technicians will need to

reformulate medication from a tablet or capsule into a liquid

• We need to know how to determine how many tabs/caps to use

Example• You are preparing a Prevacid solution that should have

the final concentation 30 mg/5 mL. If Prevacid is available as a 15 mg capsules, how many should be used to prepare 100 mL of solution?

Two ways to solve:• Determine how many mg are in the total solution, and

divide by 15 mg• Use Dimensional analysis

(Space to write from last example)

Example:• You are preparing 200 mL of a solution that contains 25

mg/10 mL. If tablets are available as 10 mg each, how many should be used to prepare this solution?

Example• You are making a solution that contains 30 tablets that are

10 mg each. If the final solution contains 150 mL, what is the concentration?

Practice• You are making a solution that contains 40 mg/5 mL. If

you are dispensing a total of 4 ounces, how many 15 mg tablets should be used?

Practice• You are making a solution that contains 15 tablets that are

20 mg each. If the final solution is 200 mL, what is the concentration (mg/mL)?

Questions?

Recipes• Some of you may end up with a recipe question• Think of these as literal recipes, such as used in cooking,

to make things easier

• Example recipe:

• Diaper Pastetriamcinolone 3 gramsnystatin 4 gramsEucerin qs 35 grams

Recipes• Diaper Paste

triamcinolone 3 gramsnystatin 4 gramsEucerin qs 35 grams

• How many grams does this recipe make?

• What do you think we do if we only have this recipe available, but need to make 50 grams?

• Enlarge it!

Recipes• Diaper Paste

triamcinolone 3 gramsnystatin 4 gramsEucerin qs 35 grams

• We can use a proportion to determine the amount of eac ingredient needed to make 50 grams total:

• Triamcinolone: =

• X = 4.3 grams

• How about for the nystatin?

Recipes• Do we need to calculate the amount of Eucerin needed for

the new recipe?

• NO:• Remember that qs means “quantity sufficient”• Therefore, after the Triamcinolone and Nystatin have been mixed

together, we would add ENOUGH Eucerin to make the final compound 50 grams

• Why might the amount of Eucerin added vary slightly each time this compound is made?

Recipe Practice• Using the same idea, REDUCE the following recipe to

determine how much of each ingredient would be needed to prepare 120 mL of the compound.

• Recipe: Magic Mouthwash• Benadryl 30 mL• Maalox 30 mL• Viscous lidocaine 30 mL• Total volume: 90 mL

Recipes Practice • Enlarge the following recipe to calculate the amount of

each ingredient needed to make 450 grams

Ibuprofen CreamIbuprofen powder 4 grams

Capsaicin 0.5 grams

Eucerin Cream qs 30 grams

Questions?

Practice: