Home' Australian Pharmacist : April 2011 Contents Vol. 30 -- April #04
Continuing Professional Development
Figure 2. Method of preparation for an oestrogen-containing
Oestrogen-containing vaginal gel
API -- oestradiol/oestriol (micronised powder)
Commercial gel base
to required volume
1. CAUTION needs to be taken when compounding hormone preparations
as they can be absorbed through the skin, mucous membranes and lungs.
Wear the appropriate laboratory clothing, mask and safety glasses and
limit the amount of drug particles, which are airborne. TIP: Compounding
on black paper will enable any residual amounts of drug to be visualised.
2. Ensure all equipment used is clean and wiped down with alcohol before
3. Accurately measure the required amount of the API.*
4. Incorporate the API by trituration with a small proportion of the gel base to
make a smooth paste.**
5. Incorporate the remaining gel base using the principle of geometric
6. Package and label.
*Note: The amount of API required might be less than that which can be
accurately weighed in the pharmacy. Pharmacists in this case may prepare a
trituration using an inert diluent, for example, microcrystalline cellulose.
**Note: Alternatively, a suitable levigating agent may be used to make a
smooth paste prior to incorporation of the API into the gel base. Levigating
agents are used with insoluble solutes to increase solubility (oestradiol and
oestriol are poorly soluble in water). TIP: Use a small amount of this agent
and ensure that it is compatible with the gel base. For example, if the gel
base is aqueous, glycerin or propylene glycol may be used, or a suitable
excipient can be chosen from the list of ingredients that are already contained
within this commercial base.
Figure 3. Example of a trituration
Case study -- Trituration
A pharmacist is required to fill a prescription for 12.5 g of a vaginal gel
containing 1 mg/g of oestradiol, therefore requiring 12.5 mg of this API. The
minimum weighable quantity of this API on the balance in their pharmacy is
50 mg. Suggest a solution to this problem.
1. Weigh 50 mg API.
Note: This is four times the required amount. 50 mg is the smallest
amount that can be accurately weighed on this pharmacy balance.
2. Mix the API with 150 mg of a suitable inert diluent, such as
microcrystalline cellulose, using the principle of geometric dilution.
Note: This gives a total weight of 200 mg.
TIP: Choose a total weight that is easily divisible by 4.
3. 50 mg of the above trituration will therefore contain 12.5 mg of the API.
50/200 x 50 = 12.5 mg
Polycarbophil is polyacrylic acid
cross-linked with divinyl glycol.13
The acidic-buffering properties of
polycarbophil are useful in vaginal
preparations since they maintain
the normal acidic pH of the vagina,
providing an unfavourable environment
for bacterial infection and allowing
the reestablishment of the normal
physiology.9 Polycarbophil has also
been reported to be effective in
the treatment of vaginal dryness,
particularly in post- and peri-
menopausal women, and is found in
the commercial product Replens.9
Gels are complex formulations
and care should be taken with the
incorporation of additional excipients
into gel bases as this may alter the
physical behaviour and compromise
their integrity. This particularly includes
excipients which may alter the pH or
the three-dimensional structure of the
gelling agent. Changes in temperature
can compromise the integrity of those
gels which are thermosensitive.10
There are commercially available gel
bases which contain a combination
of appropriate excipients in the one
product (contact your local supplier
for gel options). These products are
convenient to use and have been
formulated including preservatives
for optimum stability. A common
commercially available gel in practice
is Replens (a vaginal moisturiser)
which contains the following
ingredients: polycarbophil, Carbopol
974P, glycerin, hydrogenated palm
oil glyceride, methylparaben (methyl
hydroxybenzoate), mineral oil, sodium
hydroxide, sorbic acid and water.9
The pharmacist, in consultation with
the prescriber, may decide on the
use of various gel bases to meet
the requirements of the patient. A
simple method of preparation for an
oestrogen-containing vaginal gel using
a commercially available gel base is
shown in Figure 2.
Packaging and storage
Oestrogens should be packaged
protected from light.7 A variety of
packaging options are available
including plastic tubes combined
with an appropriate applicator device
(contact your local supplier for
packaging options). Patients may also
have a preference for a particular
packaging type. It is important that
patients are counselled on the use,
accurate measurement of a dose, and
solutions through compounding
The articles in this series are independently researched and compiled by PSA commissioned authors and peer reviewed.
Australian Pharmacist acknowledges the unrestricted support from NxGen Wholesaling.
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