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The Apothecary

Extemporaneous Prescribing Guide

Menthol and Eucalyptus Inhalation BP

Chlorinated Lime and Boric Acid Solution BP (Eusol)

Toothpaste ACH

Trichloroacetic Acid Paste APF (Upton's Paste)

Zinc and Castor Oil Ointment APF

“Extemporaneous adj. 1. spoken, performed, etc., without preparation; extempore;
2. done in a temporary manner; improvised.”
The Collins Concise Dictionary

1. What is an extemporaneous product?
2. Why use an extemporaneous product?
3. Where to find formulations?
4. How to prescribe extemporaneous products?
5. Where to get extemporaneous products and is a prescription needed?

With the ever increasing reliance on the use of commercial pharmaceutical products in clinical practice, knowledge on the use of extemporaneous products has not surprisingly declined, particularly amongst the younger generation of health care professionals.

For those who are new to the concept of extemporaneous prescribing, the following is an attempt to provide some information on extemporaneous prescribing, and examples of various formulations which you may find useful in clinical practice as alternatives. Hopefully, the information provided will also be useful to those who already prescribe extemporaneous products and perhaps clarify issues and provide new formulations for use.

What is an extemporaneous product?

An extemporaneous product, as the definition above eludes to, is a pharmaceutical product (or otherwise) which has been freshly compounded without prior preparation or in an improvised manner according to the art.

Why use an extemporaneous product?

The reasons for using extemporaneous products are many and varied. Some reasons may include:
1. The product is not available commercially;
2. Patient and/or clinician preference;
3. The concentrations of the product needs individualisation;
4. Patient and/or clinician feels extemporaneous products may be superior; and
5. Hypersensitivity to commercial products eg. preservatives.

Where to find formulations?

In Australia, the Australian Pharmaceutical Formulary and Handbook (APF), published by the Pharmaceutical Society of Australia, and the British Pharmacopoeia (BP), published by the Royal Pharmaceutical Society of Great Britain, are official and legally accepted standards for the formulation of drugs. Thus, where possible, it is recommended that these sources be used for pharmaceutical formulations. The British National Formulary (BNF) published by the British Medical Association and the Royal Pharmaceutical Society of Great Britain also provide some formulations.

In addition, many clinicians and pharmacists have their own special formulations which they often use in clinical practice. These may have been picked up through clinical experience or readings. Hospital pharmacies are another useful resource, particularly for sterile products eg. eye drops, and for highly specialised drugs.

How to prescribe extemporaneous products?

The formulation
For formulations which are specified in the APF or the BP, it is permissible to simply write the accepted name for the formulation. For example, Trichloroacetic acid paste (Upton’s paste) contains:

Trichloroacetic acid 1 part
Salicylic acid 6 parts
Glycerol 2 parts

Rather than writing the entire formulation, the prescription may state “Trichloroacetic acid paste APF” or “Upton’s paste”, the accepted synonym.

However, for personal formulations, or if the APF/BP formulations are altered in any way, then the entire formulation will need to be stated in the prescription. Using the above example, if the salicylic acid content is to be reduced to 5 parts, then the prescription will have to read (for example):

The Paste
Trichloroacetic acid 1 part
Salicylic acid 5 parts
Glycerol 2 parts

Directions for use
It is now a legal requirement for prescriptions to specify directions for use. Directions such as “mdu” or “as directed” are no longer acceptable. The APF and BP does specify directions for use for some (but not all) products and these can be followed. In addition, for personal formulations, clinical experience often dictates how often products should be used and how it should be used for maximum efficacy and tolerability. When in doubt, it may be useful to look at similiar products available commercially in the MIMS or Prescription Products Guide, or to ask the pharmacist.

Quantities
The quantity to be dispensed should also be specified. Extemporaneous products in most circumstances have an expiry date of 30 days from the date of manufacture. Thus it is recommended that quantities specified do not exceed that which may be used within that period for safety and economic reasons; or beyond the treatment duration.

The Pharmaceutical Benefits Scheme (PBS) allows for quantities of 100 g for creams, ointments and pastes, 200 mLs for lotions and mixtures, and 15 and 25 mLs for eye/ear drops and paints respectively. It should be noted that not all extemporaneous products are covered by the PBS - see the back of the PBS book for accepted products.

Using abbreviations
Many abbreviations in medicine and pharmacy are derived from latin. Thus, those who are familiar with latin should have no problems. Some common abbreviations which may be useful include:

Guttae (Gutt; gtt) = Drops eg. for eye/ear drops
Unguentum (Ung.) = Ointment
Pigmentum (pig.) = Paint
Mist. = Mixture

Similiarly, common abbreviations for pharmaceutical agents may be used eg. Ac. Sal. (Acidum Salicylicum) for salicylic acid; LPC (Liquor Picis Carbonis) for Coal Tar Solution.

Where to get extemporaneous products and is a prescription needed?

Extemporaneous products will generally be prepared by most pharmacies and for many, a prescription may not be required depending on its content eg. aqueous cream. Products which are to contain a restricted agent eg. cocaine, dithranol will require prescriptions. Prescriptions will also be required for patients who utilise the PBS. When in doubt, check with the pharmacist or provide a prescription.

The availability of extemporaneous products will generally be limited by the availability of facilities eg. sterile facilities for sterile products, and raw ingredients. It may be useful to check with the local pharmacist if ingredients are available, and provide ample notice (eg. 24 hours) for complex products to be prepared.