Reducing and Enlarging Formulas
Yewande Dayo
Student Pharmacist
Objectives
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Perform calculations to reduce and enlarge formulas for
pharmaceutical preparations stated in metric quantities
Perform calculations to reduce and enlarge formulas for
pharmaceutical preparations stated in proportional parts
Reducing and Enlarging Formulas
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Official USP-NF formulas are generally based on preparing
1000 mL or 1000g of product.
Some formulas are based on the preparation of a dosage unit
(e.g. 1 capsule) or other quantity (e.g. 100 mL).
Industrial formulas may be scaled up to quantities of
ingredients necessary to make hundreds of thousands of
dosage units in a production batch.
Thus, quite frequently, Pharmacists have to reduce or enlarge
formulas in their course of practice
This may be calculating the quantities of each ingredient
required for a smaller or greater quantity while maintaining
the correct proportion of one ingredient to the other.
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Reducing or enlarging formulas can be done by a twostep process:
1.
2.
Determine the factor that defines the multiple or the
fraction of the amount of formula to be prepared
Factor = Quantity of formula desired/ quantity of
formula given
Multiply the quantity of each ingredient in the formula
by the factor to determine the amount of each
ingredient required in the reduced or enlarged formula
Example 1
If a formula for 1000 mL contains 6 g of a drug, how many
grams of drug are needed to prepare 60 mL of the
formula
1. 60 mL/1000 mL = 0.06 (factor)
2. 6 g x 0.06 = 0.36 g, answer
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Example 2
RX
 Zinc oxide
 Pine tar
 Petrolatum
50 g
120 g
284 g
How much pine tar would be required to prepare 1 kg of the
ointment?
1. Factor = 1000 g/454 g = 2.2
2. Amount of pine tar required = 120 x 2.2 = 264 g
Example 3
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RX
Zinc oxide
50 g
Pine tar
120 g
Petrolatum q.s. ad. 284 g
How much pine tar would be required to prepare 1 kg of the
ointment?
1. Factor = 1000/284 = 3.5
2. Amount of pine tar required = 3.5 x 120 = 420 g
Example 4
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From the following formula, calculate the quantity of each
ingredient required to make 240 mL of calamine lotion.
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Calamine
Zinc oxide
Glycerin
Bentonite magma
Ca(OH)2 solution to make
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80 g
80 g
20g
250 mL
1000 mL
Example 5
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From the following formula for artificial tears, calculate
the quantity of each ingredient required to prepare a
dozen 30 mL container
Polyvinyl Alcohol
1.4 g
Povidone
0.6 g
Chlorobutanol
0.5 g
Sterile Sodium Chloride Solution, 9% ad 100 mL
Formulas That Specify Proportional Parts
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Rarely, a pharmacist may encounter an old formula with
ingredients in “parts” rather than measures of weight and
volume
The “parts” indicate a relative proportion of each
ingredient in weight or volume
Example 6
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RX
Coal Tar
Zinc Oxide
Hydrophilic Ointment
5 parts
10 parts
50 parts
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Calculate the quantity of each ingredient to make 1000g of the
ointment.
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Total parts by weight = 65
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Thus, 1000 g will contain 65 parts!!!