compounding calculations jessica johnson, pharm. d
TRANSCRIPT
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COMPOUNDING CALCULATIONSJessica Johnson, Pharm. D.
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TOPICS• Percent Concentrations• Ratio Concentrations• Determining # of tabs/caps needed to reformulate into a
liquid• Recipes
• Enlarging• Reducing
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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
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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
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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
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• 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?
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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
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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?
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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!
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Questions?
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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:
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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
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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?
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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.
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Ratio Percent Practice• Convert the ratio 1:12,500 (w/v) to a percent.
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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
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Percent Ratio Practice • Convert 0.002% to a ratio
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Questions?
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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
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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
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(Space to write from last example)
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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?
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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?
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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?
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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)?
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Questions?
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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
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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!
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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?
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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?
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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
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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
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Questions?
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Practice: