Sterility Aspects of Eye Preparations, Aseptic Processing and Choice of Preservatives

Preparations for the eye, till about 1953, were not required to be sterile which was a serious shortcoming in ophthalmic medication.

However, in the present time sterility of eye medication has been prescribed officially by the Pharmacopoeias. This applied both to the manufactured preparations as well as to the dispensed preparations.

In extemporaneous dispensing of prescriptions to sterilize a preparation may be time consuming and sometimes impractical.

Thus medication for the eye is generally dispensed in manufacturer’s sealed containers. It is essential, however, that a pharmacist though not very often required to compound and sterilize eye medication, must be familiar with every aspect of these preparations and their preservation.

Facilities for dispensing such preparations must exist in the Pharmacy and a pharmacist must receive adequate training in the techniques associated with the compounding, sterilizing and filling the containers aseptically.

Generally, a manufacturer’s original package is a small sealed sterile container. A dropper may be an integral part of the closure device or may be supplied duly packed in the carton for instilling the solution in the eye.

Once a sealed container is opened and the medication used, it becomes increasingly contaminated following each usage and therefore the supply is in a small container.

Larger packages are also manufactured for clinics and hospitals where a large number of patients call for the treatment. However, in such institutions, a separate sterile dropper is used for each patient.

In view of the unavoidable contamination, inclusion of chemical preservatives is essential in ophthalmic preparations Common preservatives are listed below.

Preparations for the eye can be sterilized by any method depending upon the nature of the drug and its stability under the conditions of sterilization. It is presumed that a pharmacist is familiar with the principles, methods and techniques of sterilization and the equipment to be used.

The most common method for sterilizing aqueous liquid preparations is with the help of steam under pressure (autoclaving). For a pharmacy a pressure cooker is good enough and sterilization can be brought about within half an hour at 12l°C and 15 lb per square inch pressure which is attainable in a pressure cooker.

Thermolabile medication can be sterilized under aseptic condition by filtering the solution through bacteria-proof filters. It is desirable to have a few varieties of filters and candles available in the pharmacy for this purpose.

A modern pharmacy is expected to have an aseptic room to carry out aseptic operations; even small pharmacies must be equipped with a glass hood for aseptic work.

Aseptic work is a specialized technique and a pharmacist is expected to master it during the period of his training so as to handle aseptic problems with confidence. A brief outline of the sources of likely contamination and aseptic operation is given below.

Two classes of pharmaceutical preparations are required to be sterile – injectables and preparations for the eye. The purpose of employing aseptic process is to eliminate the possibility of contamination with micro-organisms during preparation, packaging and testing of the medication. If the medicament is packed and sealed in such a container, which after sterlization, dose not permits contamination; there is no necessity of aseptic technique.

In other words, the heat treatment at the end of the process and the sealed container safeguard the sterility of the product till the container is opened. But in cases there such terminal heat treatment is not possible; one has to resort to aseptic processing.

Example of this type include thermo-labile drugs in solution and suspension form, thermo-labile drugs in powder form meant for dusting or for dilution just before use and thermo-labile substances to be mixed with the base as in case of eye ointments. In addition to the above requirements for preparation and packaging, aseptic handling is essential is testing the medication for sterility.

Aseptic technique precludes the possibility of contamination, which should ensure an aseptic operation. The biggest source of contamination is air.

Although atmospheric air does not provide any nutrition to the micro-organisms and thus does not promote their growth, yet it acts as an effective agency fox carrying, micro-organisms in it. It carries in itself several substances on which micro organisms get conveniently deposited e.g. dust, droplets, and droplet nuclei. The air that one breathes can hold a considerable number of micro organisms.

Other agencies that cause heavy contamination include hands, clothes, hair of the workers in the area, the working area and the equipment used.

From the above it is apparent that aseptic processing requires aseptic working condition and a good training in functioning of the pharmacist in a manner that will lead to minimal contamination.

Working conditions embody the aseptic laboratory, its furniture, services and equipment needed therein. Functioning of the pharmacist requires a consciousness to the possibility of contamination and conducting oneself in a suitable manner.