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Table of Contents
                            Pharmaceutical Compounding and Dispensing
Title Page
Copyright
Contents
Preface
About the authors
Acknowledgements
Museum of the Royal Pharmaceutical Society
British Society for the History of Pharmacy
Online material
PART 1 - History of compounding
	1 - Historical perspective
		The origins of the pharmacy profession
		Foundation of the Royal Pharmaceutical Society of Great Britain
		Pharmacy legislation
		Development of the pharmacopoeias
	2 - Obsolete dosage forms, equipment and methods of preparation
		Obsolete pharmaceutical preparations and preparative methods
		Old pharmaceutical equipment
		Old pharmaceutical containers
	3 - Historical weights and measures
		Metrication
PART 2 - Pharmaceutical forms and their preparation
	4 - Key formulation skills
		Weights and measures
		Medication strength
	5 - Extemporaneous dispensing
		Guide to general good practice requirements
		Suitable record keeping
		Equipment
		Product formulae
		Ingredients
		Storage and labelling requirements
		Pharmaceutical packaging
	6 - Solutions
		Introduction and overview
		General principles of solution preparation
		Oral solutions
		Gargles and mouthwashes
		Enemas and douches
		External solutions
		Worked examples
		Summary of essential principles relating to solutions
	7 - Suspensions
		Introduction and overview
		General principles of suspension preparation
		Oral diffusible suspensions
		Oral indiffusible suspensions
		Suspensions for external use
		Worked examples
		Summary of essential principles relating to suspensions
	8 - Emulsions
		Introduction and overview
		Formulation of emulsions
		General method of preparation of an emulsion using the dry gum method
		Stability of emulsions
		Emulsions for external use
		Worked examples
		Summary of essential principles relating to emulsions
	9 - Creams
		Introduction and overview
		Terminology used in the preparation of creams, ointments, pastes and gels
		General principles of cream preparation
		Worked examples
		Summary of essential principles relating to creams
	10 - Ointments, pastes and gels
		Introduction and overview
		Ointments
		Pastes
		Gels
		Worked examples
		Summary of essential principles relating to ointments, pastes and gels
	11 - Suppositories and pessaries
		Introduction and overview
		General principles of suppository and pessary preparation
		General method for suppository preparation
		Worked examples
		Summary of essential principles relating to suppositories and pessaries
	12 - Powders and capsules
		Introduction and overview
		Bulk powders for external use
		Bulk oral powders
		Individual unit dose powders
		Unit dose capsules
		Worked examples
		Summary of essential principles relating to powders and capsules
	13 - Specialised formulation issues
		Introduction and overview
		Posology
		Dermatological extemporaneous formulation
		Further reading
PART 3 - Product formulae
	Preface
	14 - Creams
	15 - Dusting powders
	16 - Internal mixtures
	17 - Liniments, lotions and applications
	18 - Ointments and pastes
	19 - Powders
	20 - Miscellaneous formulae
Appendix 1 - Glossary of terms used in formulations
Appendix 2 - Abbreviations commonly used in pharmacy
Appendix 3 - Changing substance names from British Approved Names to recommended International Non-Proprietary Names
	Drug names
	Radicals and groups
Bibliography
Index
                        
Document Text Contents
Page 152

Mineral oils:

Oil 3 parts by volume
Aqueous phase 2 parts by volume
Gum 1 part by weight

Aromatic (volatile) oils:

Oil 2 parts by volume
Aqueous phase 2 parts by volume
Gum 1 part by weight

These proportions are important whenmaking the

primary emulsion, to prevent the emulsion breaking

down on dilution or storage.

The quantities for primary emulsions (in parts) are

summarised in Table 8.3.

Accurate weighing and measuring of the compo-

nents in the primary emulsion are important when

making the primary emulsion to prevent the emulsion

breaking down on storage or dilution.

Wet gum method
The proportions of oil, water and emulsifying agent

for the preparation of the primary emulsion are the

same as those used in the dry gum method. The differ-

ence is in the method of preparation.

Using this method the acacia powder would be

added to the mortar and then triturated with the water

until the gum was dissolved and a mucilage formed.

The oil would then be added to the mucilage drop by

drop while triturating continuously. When nearly all

the oil has been added, the resulting mixture in the

mortar may appear a little poor with some of the oil

appearing to be absorbed. This can be rectified by the

addition of slightly more water. The trituration con-

tinues until all the oil has been added, adding extra

small amounts of water when necessary. When all the

oil has been added, the mixture is triturated until a

smooth primary emulsion is obtained.

In the main this method has fallen out of favour as

it takes much longer than the dry gum method. It

should be noted that there is less chance of failure with

this method provided the oil is added very slowly and

in small quantities. It also means that the reasons for

failure outlined belowwhen using the dry gummethod

have been eliminated.

Example 8.1 What quantities would
be required to produce 100mL of a
20% emulsion of a fixed oil?

For a 20%emulsion 20mL of the oil in 100mL

of emulsion would be required.

Therefore 4 parts would be equivalent to

20mL of oil.

Therefore 2 parts would be equivalent to

10mL aqueous phase.

Therefore 1 part would be equivalent to 5 g

of gum.

The formula for the primary emulsion

would therefore be:

Fixed oil 20mL

Aqueous phase 10mL

Gum 5g

General method of preparation of
an emulsion using the dry gum
method

It is relatively easy for an emulsion to crack, resulting

in a failed product. Remember the following points are

critical when preparing emulsions:

* Clean, dry equipment – All equipment should be

thoroughly cleaned, rinsed with water and dried

carefully before use, particularly measures,

mortars and pestles.
* Accurate quantities – Accurate quantities are

essential. Check weighing/measuring technique

and minimise transference losses (e.g. allow oil to

drain from measure).
* Have all ingredients ready – Correct rate of

addition is important. Ingredients for the primary

emulsion should all be weighed and measured

before starting to make the product.

Table 8.3 Ratio of oily phase to aqueous phase to
gum in a primary emulsion

Type

of oil

Examples Oil Aqueous Gum

Fixed Arachis Oil BP

Castor Oil BP

Cod Liver Oil BP

4 2 1

Mineral Liquid Paraffin BP 3 2 1

Volatile Cinnamon Oil BP

Peppermint Oil BP

2 2 1

Emulsions | 135

Page 153

The preparation of an emulsion has two main

components:

* Preparation of a concentrate called the ‘primary

emulsion’.
* Dilution of the concentrate.

Preparation of the primary emulsion

1 Measure the oil accurately in a dry measure.
Transfer the oil into a large dry porcelain mortar,

allowing all the oil to drain out.

2 Measure the quantity of aqueous vehicle required
for the primary emulsion. Place this within easy

reach.

3 Weigh the emulsifying agent and place on the oil
in the mortar. Mix lightly with the pestle, just

sufficient to disperse any lumps. Caution –

overmixing generates heat, which may denature

the emulsifying agent and result in a poor product.

4 Add all of the required aqueous vehicle in one
addition. Then mix vigorously, using the pestle

with a shearing action in one direction.

5 When the product becomes white and produces a
‘clicking’ sound the primary emulsion has been

formed. The product should be a thick white

cream. Increased degree of whiteness indicates a

better quality product. Oil globules/slicks should

not be apparent.

Dilution of the primary emulsion

1 Dilute the primary emulsion drop bydropwith very
small volumes of the remaining aqueous vehicle.

Mix carefully with the pestle in one direction.

2 Transfer emulsion to a measure, with rinsings.
Add other liquid ingredients if necessary and

make up to the final volume.

See Emulsions video for a demonstration of the

preparation of an emulsion.

Problems encountered when making the
primary emulsion
The primary emulsion does not always form correctly

and the contents of the mortar may become oily, thin

and translucent. This is because of phase inversion.

The oil-in-water emulsion has become a water-in-oil

emulsion that cannot be diluted further with the aque-

ous vehicle. The product has failed and must be

restarted. Reasons for this include:

* inaccurate measurement of water or oil
* cross-contamination of oil and water
* use of a wet mortar
* excessive mixing of the oil and gum
* poor-quality acacia
* insufficient shear between the head of the pestle

and the mortar base
* too early or too rapid dilution of the primary

emulsion.

Stability of emulsions

Emulsions can break down through cracking, cream-

ing or phase inversion (Table 8.4).

Cracking
This is the term applied when the disperse phase coa-

lesces and forms a separate layer. Re-dispersion can-

not be achieved by shaking and the preparation is no

longer an emulsion. Cracking can occur if the oil turns

rancid during storage. The acid formed denatures the

emulsifying agent, causing the two phases to separate.

See Emulsions video for an example of a

cracked emulsion.

Table 8.4 Summary of the problems encountered
in emulsion preparation

Problem Possible reason

for problem

Can the emulsion

be saved?

Creaming –

Separation of the

emulsion into two

regions, one

containing more of

the disperse phase

Lack of stability of

the system.

Product not

homogeneous

The emulsion will

reform on shaking

Cracking – The

globules of the

disperse phase

coalesce and there

is separation of the

disperse phase into

a separate layer

Incompatible

emulsifying agent.

Decomposition of

the emulsifying

agent. Change of

storage

temperature

The emulsion will

not reform on

shaking

Phase inversion –

From o/w to w/o or

from w/o to o/w

Amount of

disperse phase

greater than 74%

The emulsion will

not reform on

shaking

o/w, oil in water; w/o, water in oil.

136 | Pharmaceutical forms and their preparation

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