Dispensing Techniques
Compounding and Good Practice
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Compounding (Extemporaneous Dispensing)
• Definition: A small-scale manufacture of medicines from
basic ingredients in the community or in hospital pharmacy (
vs. medicines manufactured
by the pharmaceutical
industry).
• Extemporaneous dispensing should only be used when
medicines are not available commercially in the market:
 Low demand.
 Requires an individualized dose, e.g. paediatric.
 Requires an individualized formulation for a patient.
The working environment
• Organization
• Cleanliness
The bench, the equipment, utensils & the container. Lack of
cleanliness can cause contamination of the preparation with other
ingredients or a microbial contamination.
• Appearance
A clean white overall, closed, hair tied up.
• Documenting procedures and results
 Keeping comprehensive records for a minimum of 2 years (ideally 5
years) and include the formula, the ingredients and quantities used,
their sources, batch numbers and expiry date.
 The record for a prescribed item should also include the patient and
prescription details and date of dispensing.
 Methodical approach.
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EQUIPMENT
A. Weighing
• Non-automatic and automatic weighing
equipment.
• Non-automated dispensing balances include
mechanical beam and electronic top-pan
balances.
• Three types of balances have traditionally
been used in dispensing; class A (50mg to 1g),
class B (the most commonly used; 100mg to
50g), and class C (1g to 2kg).
•
Class B prescription balances are designed for
the weighing of medicinal or pharmaceutical
substances required in filling of prescriptions
or in a small scale compounding. (Also known
as Class B dispensing balance).
EQUIPMENT
Torbal torsion balance ( class B) and Ohaus electronic
balance.
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EQUIPMENT
Set of metric weights
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EQUIPMENT
• When weighing, some important rules to ensure good
dispensing practice:
• Use balances on a level surface (level indicator device).
• Balances must be balanced before use, with any
indicators reading zero.
• Keep the balance in a draught-free environment, clean
and free from debris.
• When using a top-pan balance, an appropriate container
(weighing boat) or piece of paper and auto-zero to cancel
its weight.
• If using a solid material which requires to be size reduced
(ground) or sieved, always ensure that this is carried out
before weighing the required quantity.
• As far as possible never split quantities and do two
weightings, as this will increase the inaccuracies.
• If a quantity less than the legal minimum is needed, it is
necessary to weigh the minimum weight allowable (or
more) and make an excess of the product or prepare it by
trituration.
EQUIPMENT
B. Measuring liquids
• Liquid
measures:
Conical
measures
and
cylindrical
measures.
• Measuring small volumes: by
small conical measure (min.
measurable vol for a 10 mL
conical is 1 mL), by graduated
pipettes (5 mL to 0.1mL), and by
trituration (for smaller volumes).
EQUIPMENT
• The level of liquid is read to the
bottom of the meniscus.
• The measure is vertical when
reading the meniscus; if not
considerable errors in quantities
can occur especially with
conical
where
the
error
increases with height because of
the slope of the sides.
Volume error differentials due to
instrument diameters
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EQUIPMENT
• Never use more than one measure  increases error.
• Select the smallest measure that will hold the desired
volume.
• The measure is thoroughly drained (material can be left in
the measure).
• If the substance being measured is so viscous difficult to
drain the measure effectively  measurement by difference
(pouring excess into the measure and then pouring off the
liquid until only excess volume remains).
• Rules for good dispensing practice (label position and the
cap of the container).
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EQUIPMENT
C. Mixing & Grinding
Mortar and pestle
Glass mortar and pestle
• Used for small quantities: Useful for dissolving small quantities of
ingredients, for mixing small quantities of fine powders
• Suitable for size reduction of friable materials (such as crystals).
• Used for the mixing of substances such as dyes which are absorbed
by and stain composition or porcelain mortars.
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EQUIPMENT
Porcelain or composition mortars and pestles
• Larger than the glass variety and have a rougher surface.
• Ideal for size reduction of solids and for mixing solids and
liquids, as in the preparation of suspensions and
emulsions.
• For size reduction select
proper type.
• For mixing purposes:
- sufficient space is
required for adequate
mixing
- Rotate pestle in both
directions
EQUIPEMENT
Filters
Filters are used when clarification of a liquid is required.
Filter paper
• Filter paper has the disadvantages of introducing fibers into the
filtrate and may also absorb significant amounts of active ingredient.
Such disadvantages are less likely to happen with the following
types.
Membrane filters
Sintered glass filters
• These do not shed fibers, are easy to clean and can be used for
substances which attack filter paper such as potassium
permanganate and zinc chloride.
A filter with a pore size 15–40 µm (grade 3) is suitable for most
solutions. They will pass through by gravity, although large volumes
may be slow and need the assistance of a vacuum. A grade 4 filter
(pore size 5–15 µm) requires a vacuum.
Filters
Sintered glass filter
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EQUIPMENT
D. Heat Sources
•Bunsen (gas) burners
The Bunsen burner, used for heating laboratory equipment and
chemicals. The flame can reach temperatures of
1,500°C/2,732°F and is at its hottest when the collar is open.
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EQUIPMENT
• Water-baths: These are used when melting
ointment bases or preparing suppositories
• Electric hot plates: Used for melting and
heating and have the advantage of
thermostatic controls.
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Manipulative techniques
Correct equipment + Appropriate technique = Good Compounding
Practice
* Mixing
The goal of any mixing operation should be to ensure that even
distribution of all the ingredients has occurred.
•Mixing of liquids: Simple stirring or shaking (the degree depends
on the viscosity of liquids).
•Mixing solids with liquids: stirring rod (solution), pestle and
mortar (suspension). Consider size reduction to speed up
dissolution process or enhance the distribution of solid through
out the liquid.
•Mixing solids with solids: mortar and pestle, “doubling up”
procedure.
•Mixing semi-solids
rubbing them on an ointment slap using a spatula (may need
doubling up).
The fusion method using a porcelain evaporating basin.
Manipulative techniques
• Tared containers
• For what purpose?
• How to tare a bottle?
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SELECTION OF INGREDIENTS
•
•
•
•
•
Reputable supplier.
Good storage conditions.
Check on expiry dates.
Variety of forms.
Synonyms.
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SELECTION OF INGREDIENTS
• Variety of forms:
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Selection of ingredients
• Synonyms:
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Concentrated waters
• Liquid preparations for oral use are often flavored
to make them more palatable for the patient. In
extemporaneously prepared products the
flavoring is frequently a flavored water, e.g.
peppermint water, aniseed water.
• All concentrated waters have the same dilution
factor, i.e. 1 part of concentrate plus 39 parts of
water to give 40 parts of flavored water.
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PROBLEM SOLVING IN
EXTEMPORANEOUS DISPENSING
• ‘Official’ preparations
• The application of simple scientific knowledge; physical
properties.
• Solubility: are the ingredients soluble in the main vehicles,
the particle size, are they present in a lumpy or granular form.
If the substance is not soluble, a suspension or an emulsion
where one material is an oil will be produced.
• Volatile ingredients
• Viscosity
• Expiry date.
e.g. The following prescription is received:
• Sodium Bicarbonate Ear Drops BP, Send 10 mL.
• Formula:
Sodium bicarbonate 500 mg (sol 1 in 11 of water)
Glycerol 3 mL (viscous liquid)
Freshly boiled and cooled water to 10 mL (quantity of water in
ear drops is app. 6.5 mL)
COUNTING DEVICES For Tablets and Capsules
• Various methods can be used for this counting:
• The manual method.
• A counting triangle (for pills) and capsule counter
are the best.
• A perforated counting tray.
• An electronic counter: Electronic balances, Photoelectric
cell counters.
• medicines must not be touched by hand.
• The equipment should also be carefully cleaned
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before use.
Counting triangle
http://iforg.com/blog/?p=17
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Capsule counter
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Perforated Counting Tray
http://www.adelphi-coldstream.uk.com/products/pharmacyl-dispensing-equipment/tablet-capsulecounters/tumatic-capsule-counter.html
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Key Points
• Extemporaneous dispensing should only be
used when manufactured medicines are not
available.
• Accurate dispensing requires clean, neat
methodical work.
• Comprehensive records of extemporaneous
dispensing are required to be kept for at least
2 years.
• Electronic balances are increasingly being used
in extemporaneous dispensing.
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Key Points
• Do not use a balance to weigh less than its
minimum weighable quantity.
• Ensure that liquid measures comply with the
Weights and Measures Regulations.
• Always use the bottom of the meniscus when
measuring liquids.
• Viscous liquids should be measured ‘by
difference’.
• Pipettes are used to measure volumes between
0.1 mL and 5 mL.
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Key Points
• Select the smallest measure for the volume of
liquid to be measured.
• A glass mortar and pestle can be used for size
reduction of friable materials and mixing small
quantities of fine powder.
• A porcelain mortar and pestle is used for larger
quantities, for mixing solids and liquids, making
emulsions and for size reduction.
• ’Doubling-up’ is used for mixing a small quantity
of powder with a larger quantity.
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Key Points
• Confusion can arise with different forms of the
same material and the use of synonyms.
• Concentrated waters are diluted 1 part with 39
parts of water for use as single strength.
• Simple problem-solving techniques can produce a
satisfactory method of dispensing a product.
• Tablets and capsules can be counted manually, or
by using a triangle, capsule counter, counting tray
or an electronic counter.
• Tablets and capsules should not be counted in the
hand.
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