REDUCTION AND ENLARGEMENT

OF FORMULAS

INTRODUCTION

Most of the preparations made in a

pharmacy are from proven formulas

that have been tested and are listed in

the Pharmacopeia/National Formulary

as official formulas.

These formulas list the amount of each

ingredient needed to make a certain

amount of the preparation.

It is necessary to reduce or enlarge a

formula to satisfy the needs of your

pharmacy.

Sample Problem:

Calculate the amount of each ingredient

needed to make 240 ml of Peppermint

Spirit.

Peppermint Spirit

Peppermint Oil............ 100 ml

Peppermint Powder.........10 g

Alcohol.....qsad.......... 1000 ml

23

Copying Formula

100 ml

10 g

1000 ml

Peppermint Oil

Peppermint Powder

Alcohol.....qsad

Rx

For

240 ml

For

1000 ml

e.g. 1

Peppermint Spirit

Reduction of formula

e.g 2

Calculate the amount of each

ingredients needed to produce 100

ml of Codeine Linctus B.P.C.

Refer to formula in B.P.C, then copy;

note that in BPC, the final volume is

1000 ml; - reduction of formula

26

Syrup B.P. to 1000 ml

Lemon syrup 200 ml

Distilled water 20 ml

Chloroform spirit 20 ml

Benzoic acid 20 ml

Tartrazine compound 10 ml

solution

Codeine phosphate 3 g

For 100

ml

Rx 1000 ml

27

Syrup B.P. to 1000 ml 100.0 ml

Lemon syrup 200 ml 20.0 ml

Distilled water 20 ml 2.0 ml

Chloroform spirit 20 ml 2.0 ml

Benzoic acid 20 ml 2.0 ml

Tartrazine compound 10 ml 1.0 ml

solution

Codeine phosphate 3 g 0.3 g

For 100

ml

Rx 1000 ml

Note that Codeine phosphate is in

powder form; -

First dissolve codeine phosphate in water

Then add in other ingredients

Finally add syrup B.P to 100 ml (final

volume

29

Enlargement of formulas

Distilled water to 10 ml

Chloroform double strength 5 ml

Peppermint emulsion 0.25 ml

concentrate

Sodium bicarbonate 0.5 g

Light Magnesium Trisilicate 0.5 g

Light Kaolin 2 g

For

250 ml

Rx

Calculation of Concentration

in Percentage

Term percent (%)refers to

‘by the hundreds’ or ‘in a hundreds’

Also can be expressed in ratio

50% means 50 parts in 100.

In pharmaceutical; 3 types of

percentage

Weight-in-volume (w/v)

Volume-in-volume (v/v)

Weight-in-weight (w/w)

32

Definition of Percentage

the number of millimeters of a

constituent in 100 mL of

solution/liquid

preparation.

% v/v

According to USP

the number of grams of a

constituent in

100 g of solution or preparation.

% w/w

the number of grams of a

constituent in 100 ml of

solution/liquid preparation.

% w/v

34

Example of percentage

1 %

1 part in 100 ml of solution

- 1 grams of solute in sufficient amount

of solvent to produce 100 ml

preparation.

* note that 1 % is NOT 1 gram of

solute in 100 ml of solvent.

35

Calculation of percentage

1:400 1 x 100 % = 0.25 %

400

1:1000 1 x 100 % = 0.1 %

1000

2:2500 ?

4:10,000 ?

36

Calculation of percentage

w/v

Calculate the amount of Sodium Chloride

needed to produce 1.5 L of Sodium

Chloride 0.9% Solution.

Answer:

0.9% - 0.9 g of NaCl in 100 ml of solution

In 100 ml; contains 0.9 g NaCl

In 1500 ml; contains ? g NaCl

37

Therefore:

In 1500 ml 0.9 g x 1500 ml

100

= 13.5 g

Amount Sodium Chloride needed is 13.5 g

- 13.5 g NaCl to be completely dissolved

in a small part of water, then add the

remaining water up to final volume

(1500 ml)

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