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205
Dosage Forms
Determine the concentration of iodine as stated in the BPC
and calculate the amount of soft paraffin required to produce a
product of the required strength.
Warm the required amount of yellow soft paraffin to 40°C in
a water bath. To this add the dissolved iodine with continuous
stirring.
Pour the mixed mass into a warm container and allow to
cool without stirring. Otherwise air will be entrapped and the
product will become opaque.
4. Emulsification Method
An emulsion system must contain an emulsifying agent if they
are to remain stable for sufficiently long time. Water soluble
soaps were commonly used as emulsifiers for semisolid oil
in water emulsions. The viscosity of ointments or creams
prevents coalescence of the emulsified phases and helps
to stabilize the emulsion. The addition of cetyl alcohol and
glyceryl monostearate tends to stabilize the semi-solid oil in
water emulsion whereas addition of polyvalent ions such as
magnesium, calcium and aluminium tend to stabilize water
in oil emulsions. Nearly all semi-solid creams and emulsified
ointments require a combination of emulsifiers. Due to this
reason a combination of triethanolamine stearate soap and
cetyl alcohol is used as an emulsifier in oil in water emulsions
and a combination of bees wax and divalent calcium ions is
used as an emulsifier for water in oil emulsions.
The non-ionic emulsifiers like glyceryl monostearate,
glyceryl monooleate, propylene glycol stearate, etc., are used
for oil in water as well as water in oil emulsified semi-solids
because they are compatible with most of the drugs. They can
be used with strongly acidic salts or with strong electrolytes.
General Method of Preparation
In the preparation of ointments having an emulsion type
formula, e.g., cold cream, the general method of preparation
involves the melting process as well as an emulsification
process.
In this method the water immiscible components such as
oils, fats and waxes are melted together over water bath at a
Introduction to Pharmaceutics
206
temperature of 70°C in an open vessel. Separately, the aqueous
solution of all of the heat stable, water soluble components is
heated to almost the same temperature as that of melted bases.
Then this solution is slowly added to the melted bases, with
continuous stirring until the product cools down and a semi-
solid mass in obtained.
It is very important to heat the aqueous liquid to almost
the same temperature as that of the melted bases otherwise
high melting point fats and waxes will immediately solidify on
addition of cold aqueous solution to the melted bases or vice
versa, and a lumpy product will be obtained.
CREAMS
Creams are viscous semisolid ointment like preparations but
have lighter body than the ointments. They may be oil in
water type (aqueous creams) or water in oil type (oily creams)
emulsions. Due to the presence of water soluble bases in oil in
water type cream they can be easily removed from the skin and
clothings. The aqueous creams have a tendency to bacterial and
mold growth, therefore, a preservative must be added. Even if
a preservative has been incorporated care must be taken for
complete cleanliness of the apparatus used in the manufacture
of creams and containers used for packing the creams. If this
precaution is not observed and a cream contaminated with
microorganisms is applied to the broken skin may produce
infection in the patient.
Preparation of Creams
To prevent any contamination with micro-organisms the
apparatus used in the preparation of creams must be thoroughly
cleaned with soap and water and rinsed with freshly boiled
and cooled water and finally dried in the oven. All hygienic
precautions should be taken throughout the preparakon and
final transfer into the containers.
Containers and Storage
Creams should be supplied in well closed containers, which
should prevent evaporation and contamination. They should
207
Dosage Forms
be stored in a cool place. The collapsible tubes made of metals
or plastics are most suitable for packing the creams. Ointment
jars can also be used. Aluminium tubes are not suitable for
packing creams which are preserved with an organic mercury
compound.
PASTES
Like ointments, pastes are the semisolid preparations meant
for external application to the skin. They differ from ointments
that they generally contain a large amount of finely powdered
solids such as starch, zinc oxide, calcium carbonate, etc.
Due to the presence of these substances they usually become
quite thick and stiff than the ointments but are less greasy than
ointments. Due to the presence of large amount of solids they
are less attractive cosmetically than ointments.
Since pastes are stiff they do not melt at ordinary
temperature thus forming and holding a protective coating
over the areas to which they are applied. They soothen the
inflamed and raw surfaces and in particular minimize the
damage done by scratching in itching conditions such as
chronic eczema. It is easier to stick the pastes to the diseased
areas rather than ointments which are generally less viscous
than pastes and tend to spread onto the healthy skin which
may result in sensitivity reactions if the preparation contains a
powerful medicament such as dithranol.
Pastes are prepared in the same manner as that of
ointments but when a levigating agent is to be used to mix the
components and to make the preparation smooth, a portion of
the base should be used as levigating agent rather than a liquid
like mineral oil that would soften the paste.
Pastes were originally formulated on the principle that the
high contents of powder substances would absorb exudate but
it is unlikely that a powder which has been specially wetted
with oil will be able to absorb an aqueous liquid. ·
Pastes can be applied to the affected part with the help of a
spatula or they may be spread on any of the dressing material
and then applied. They are not removed from the site of
Introduction to Pharmaceutics
208
application for quite a long time. The pastes are not suitable
for application to the scalp because they are very difficult to
remove from the hair.
Zinc and salicylic acid paste which is also known as
Lessar’s paste is the most commonly used paste. Medicaments
incorporated in zinc and salicylic acid paste are less active
than when included in ointments. Higher concentrations
of powerful medicaments such as dithranol may therefore
be tolerated if they are combined in zinc and salicylic acid
paste.
R
x
Starch, finely sifted 24 gm
Zinc oxide, finely sifted 24 gm
Salicylic acid, finely sifted 2 gm
White soft paraffin 50 gm
Make a paste. Send 25 gm.
Label: The Lassar’s paste.
Type: Paste with semisolid base prepared by fusion method.
Procedure: Melt the white soft paraffin on water bath.
Incorporate the starch zinc oxide and salicylic acid which has
been previously sifted through sieve no. 120. Stir until cold
and homogeneous paste is obtained.
R
x
Dithranol 0.1 gm
Zinc and salicylic acid paste q.s. 100 gm
Make a paste. Send 25 gm.
Label: The dithranol paste.
Type: Paste prepared by trituration method.
Procedure: Warm the ointment slab because this preparation is
best prepared on warm ointment slab. Triturate the weighed
amount of dithranol with a small quantity of zinc and salicylic
acid paste until smooth and complete dispersion is obtained.
Gradually add the remainder of the zinc and salicylic acid
paste with constant trituration until whole of it is added. Check
the preparation to ensure that the dithranol is completely
dispersed.
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Dosage Forms
Bases for Pastes
The bases used for the preparation of pastes are as follows:
Hydrocarbon bases
Water miscible bases
Water soluble bases.
Hydrocarbon Bases
Soft paraffins and liquid paraffin are commonly used bases
for the preparation of pastes. Compound zinc paste and
compound zinc and salicylic acid paste are prepared with soft
paraffin base. They are used in eczema and psoriasis either
alone or along with coal tar and dithranol. Coal tar paste is
used for treating eczema whereas dithranol paste is used for
ringworm or psoriasis. Liquid paraffin is used as a base in
compound aluminium paste which is used as skin protectant.
R
x
Zinc oxide, finely sifted 25 gm
Starch, finely sifted 25 gm
White, soft paraffin 50 gm
Make a paste. Send 25 gm.
Label: Spread thickly on white lint and apply to the affected
area.
Type: Paste with semi-solid base prepared by fusion and
trituration method.
Procedure: Separately pass the zinc oxide and starch through
sieve no. 120. Melt the white soft paraffin on water bath.
Mix the required weight of powders in a warm mortar. Add
small amount of melted base with continuous trituration until
smooth. Gradually add remainder of the base and mix until
cold and uniform paste is obtained.
Uses: It is used as an antiseptic paste.
Note:
1. Warm mortar is used because it is much easier to manipulate
the paste in warm mortar .
2. This preparation is also known as compound zinc paste.
R
x
Aluminium powder 20 gm
Introduction to Pharmaceutics
210
Zinc oxide 40 gm
Liquid paraffin 40 gm
Make a paste. Send 25 gm.
Label: The compound aluminium paste.
Type: Paste with liquid base prepared by trituration method.
Procedure: Mix aluminium powder and zinc oxide in a mortar.
To this incorporate liquid paraffin and triturate thoroughly
until smooth.
Water Miscible Bases
Emulsifying ointment is used as a base for resorcinol and
sulphur paste. This paste is used in the treatment of dandruff,
therefore, it should be easily removed from the hair, hence
emulsifying ointment base is used.
R
x
Resorcinol, finely sifted 1.25 gm
Precipitated sulphur 1.25 gm
Zinc oxide, finely sifted 10.00 gm
Emulsifying ointment 12.50 gm
Fiat: Pasta. Mitte 50 gm.
Type: Paste containing semi-solid base and prepared by
trituration method.
Procedure: Pass separately the resorcinol, precipitated sulphur
and zinc oxide through sieve no 120 and mix the weighed
quantities of these substances with a portion of emulsifying
ointment until smooth. Gradually add the remainder of the
emulsifying ointment with thorough trituration until smooth.
Uses: It is used in the treatment of dandruff, psoriasis (chronic
skin disease in which red scaly patches develop), eczema and
other skin diseases.
Emulsifying wax is used in the preparation of zinc and coal
tar paste which helps in easy dispersion of the coal tar as well
as easy removal from the skin after use.
Magnesium sulphate paste is prepared by using glycerin
as base to which phenol is added. This paste is used for the
treatment of boils because of the powerful osmotic effects of
magnesium sulphate and glycerin.
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Dosage Forms
Titanium dioxide paste is prepared by using glycerin and
water as base. This paste is a suspension which contains
titanium dioxide, zinc oxide, light kaolin, red ferric oxide,
glycerin and water. It is useful for absorbing exudates from
weeping skin conditions.
Water Soluble Bases
Water soluble bases are prepared from mixtures of high and
low molecular weight polyethylene glycols. The polyethylene
glycols with low molecular weight are liquid in nature whereas
the polyethylene glycols with a moderately higher molecular
weight are semisolid and polyethylene glycols with higher
molecular weight are solids. Suitable combinations of high and
low molecular weight polyethylene glycols are mixed together
to get a product of desired consistency which soften or melt
when applied to the skin. These bases are water soluble because
of the presence of many polar groups and ether linkages.
Water soluble dental paste containing neomycin sulphate is
prepared with macrogol base. Another paste contains sodium
carboxy methyl cellulose, pectin and gelatin is plastibase.
Methods of Preparation of Pastes
Like ointments, pastes are prepared by trituration and fusion
methods. Trituration method is used when the base is liquid
or semisolid while fusion method is used when the base is
semisolid and/or solid in nature. These two methods have
already been discussed in detail under methods of preparation
of ointments.
Preservation of Pastes
Pastes which contain water as one of the ingredients (e.g.,
titanium dioxide paste) or fermentable ingredients, must be
suitably preserved by adding anti-microbial preservatives.
They should be stored in air-tight containers so as to prevent
evaporation of moisture present in the paste.
Introduction to Pharmaceutics
212
GELS
Jellies are thin transparent or translucent, non-greasy pre-
parations meant for external application to the skin. They
are similar to mucilages because they are prepared by using
gums but they differ from mucilages in having jelly like
consistency. They are used chiefly on mucous membranes for
their lubricating, antiseptic or spermicidal purposes. Jellies are
also used for lubricating surgical gloves, catheters and rectal
thermometers. Vaginal jellies and contraceptive jellies are also
commonly used.
Since jellies contain carbohydrates and lot of water as base
therefore they are prone to microbial growth so they must be
suitably preserved. The commonly used gelling agents for the
preparation of jellies are tragacanth, sodium alginate, starch,
pectin, gelatin, methyl cellulose, carbomer, polyvinyl alcohols,
etc.
SUPPOSITORIES
Suppositories are special shaped solid dosage form of
medicament meant for insertion into body cavities other
than mouth. They may be inserted into rectum, vagina or
the urethra. These products are so formulated that after
insertion, they will either melt or dissolve in the cavity
fluids to release the medicament. Suppositories vary in
shapes, sizes and weights. Generally suppositories weighing
1 to 2 gm are prepared. Cocoa butter or glycerogelatin is used
as base.
Uses
Suppositories are used for any one of the three different
purposes.
1. To produce local action. ·
2. To produce systemic action.
3. To produce mechanical action on the lower bowel and
facilitate evacuation in the treatment of haemorrhoids, anal
irritation, constipation, etc.
Suppositories are convenient mode of administration of
drugs which irritate the gastrointestinal tract, cause vomitting,
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Dosage Forms
are destroyed by the hepatic circulation, or are destroyed in the
stomach by pH changes, enzymes, etc.
They can be easily administered to children, old persons
and to unconscious patients who cannot swallow the drugs
easily.
The rectal suppositories may be used for lubricating, sooth-
ing, antiseptic, local anaesthetic action or for astringent effect.
Therefore, they may contain antiseptics, local anaesthetics,
astringents, hormones and steroids. The rectal suppositories
meant for systemic effect contain analgesics, antispasmodics,
sedatives and tranquilizers.
The lower portion of the rectum affords a large absorption
surface area from which the soluble substances can pass
quickly and reach the venous circulation directly and rapid
action of the drug is produced. However, the rate and extent
of absorption of the drugs depends upon the nature of the
base in which they have been incorporated. The maximum
therapeutic effect is produced if the drug incorporated is in the
finely divided state, evenly distributed throughout the base
and in a readily absorbable form.
The rectal suppositories are extensively used as a mechanical
aid to bowel evaluation which produce its action by irritating
the mucous membrane of the rectum or by lubricating action.
The glycerin suppositories are representative example of
evacuant suppositories.
Types of Suppositories
Rectal suppositories: These are meant for introduction into
the rectum for their systemic effect. They are tapered at
one or both ends and usually weigh about 2 gm. The rectal
suppositories meant for children are smaller in size and
weight than the adult suppositories. They usually weigh
about 1 gm.
Vaginal suppositories: They are also known as pessaries and
are meant for introduction into the vagina. They are larger
than rectal suppositories and vary in weight from 3 to
6 gm or more. The vaginal suppositories may be conical,
rod-shaped or wedge-shaped. They are exclusively used
for their local action on the vagina.
Introduction to Pharmaceutics
214
Special shaped suppositories are manufactured and are
supplied with applicators to facilitate insertion into the
vagina. Nowadays a few special tablets and capsules, oval
or suppository shaped are prepared for use in the vagina
and are known as vaginal tablets and vaginal capsules
respectively.
Urethral suppositories: They are also known as urethral
bougies and are meant for introduction into the urethra.
They are long, thin and cylindrical forms rounded on one
end. Their weight varies from 2 to 4 gm and length from 2
to 5 inch. Urethral suppositories are very rarely used.
Nasal suppositories: They are also known as nasal bougies
or buginaria and are meant for introduction into the nasal
cavity. They are similar in shape to urethral bougies. Their
weight is about 1 gm and length 9–10 cm. They are always
prepared with glycero-gelatin base. ·
Ear cones: They are also known as aurinaria and are meant
for introduction into the ear. They are very rarely used.
Generally theobroma oil is used as a base, prepared in an
urethral bougies mould and cut according to the required
size.
LINIMENTS
Liniments are liquid or semi-liquid preparations meant for
external application to the skin. They contain substances
possess ing analgesic, rubefacient, smoothing or stimulating
properties. Liniments are usually applied to the skin with
friction and rubbing of the skin. They should not be applied
to the broken skin. Liniments should be dispensed in coloured
fluted bottles in order to distinguish from preparations meant
for internal use.
The bottle should be labelled “For external use only.”
Examples are methyl salicylate liniment, turpentine
liniment, white liniment.
Storage: Liniments should be stored in tightly closed containers.
The containers must bear a label ‘’For external use only.” and
“Shake the bottle well before use.”