All openings except the openings for entry need perfect sealing and horizontal surfaces including windows should be eliminated. These surfaces may allow retention of dust and may create problems.
The structure should be tight enough to prevent infiltration of uncontrolled air. All exposed surfaces should be smooth and impervious, easily cleanable and in no way prone to settling of dust upon them.
The surfacing material should not be susceptible to hold dust, flaking or chalking under normal operative procedures. Uncoated smooth surfaces e.g. stainless steel, aluminium and chromium plating, plastic laminates and plastic films make satisfactory surfaces. Cement concrete is a very undesirable surface.
Air-conditioned Atmosphere
In view of the sealed structure, preventing any source of entry of air, air conditioning is essential. Since no special requirement of temperature and humidity are prescribed, conventional air conditioning may be suitable enough. It is however preferable to have the humidity on the lower side to avoid contamination by the perspiration of the workers.
Air cleaning part of the air conditioning system is a critical factor as the nature of the atmospheric air may differ considerably from time to time. Cooling and heating coils, humidity control apparatus, reheat coils; blowers etc. are the equipment that should be of standard specifications.
However, the fans selected should be such that can provide high pressure. The room has to be constantly maintained under positive pressure to prevent inlet of air from entry point whenever it is opened. Dust, temperature and humidity control are interdependent functions.
Dust control is impossible without confining the area. Confined space is unlivable without air-conditioning. If temperature and humidity are controlled by air conditioning, dust control measures are automatically taken care of.
Cleaning of Air
Cleaning of air is the key factor of the aseptic processing. The usual approach is a combination of the conventional cleaners e.g. regular filters or electronic air cleaners located within the system and some kind of super-interception or an ultra cleaner located down stream from all coils, blowers etc.
Bactericidal equipment is incorporated in the assembly for providing sterile air in addition to be devices stated above. The air in the aseptic area should be free from fibers, dust and microbes. This can be conveniently achieved by the use of High Efficiency Particulate Air (HEPA) filters which can remove particles up to 0.3 µm with an efficiency of 99.7% or more.
HEPA filters made use of in Laminar Air Flow in which air moves with uniform velocity along parallel lines with minimum of eddies. The air flow can be either horizontal or vertical and 100 ± 10 ft/min. is considered to be the minimum effective air velocity. Such laminar flow stations and work benches are commercially available and should find immense use in compounding and dispensing practice.
Air Distribution
Materials of construction for the air distribution system should be made of non-rusting and non- flaking materials (e.g. ducts, air outlets etc.). Duct insulation, if needed, should be applied on the outer side and only on the ducts that are located out of the clean area. Joints and other fittings, if any, should be sealed to prevent leakage and contamination. Air distribution is also employed for 'washing' the workers off dust who enter the sterile area. These are called air showers which are strictly blasts or air directed on the person to remove dust.
Controls
Conventional controls are used in the system for regulating humidity and temperature. Sometimes greater pressure may have to be maintained in critical areas and for this purpose additional controls may have to be installed. Interlocks may be required between the sterile area and the entrance or passing doors. In a highly elaborate system, alarm circuits are introduced to warn against the malfunctioning or inadvertent misuse of the air locks.
Instruments
Highly sophisticated instrumentation has to be installed which constantly or intermittently monitors and samples the clean atmosphere for analyzing its cleanliness. These devices immediately indicate the contamination, if any.
Furniture
Seating, work tables, racks etc. are essential requirements of furniture inside he clean area and have to be specially designed and built to meet certain rigid specifications. Adjusting mechanisms on the chairs should either not exist or ought to be sealed. These may be potential dust setting surfaces.
Conventional upholstering of the chairs is completely out of question. Dust catching surfaces should be minimum and all parts should be readily cleanable and resistant to the action of the cleaning agents. Worker comfort is a very important factor in a confined area. The requirements of the job in a sterile room keep the workers chained to the work over long periods of time continuously without leisure and with minimum exits from the room and thus warrants high degree of comfort for carrying out the critical operations.
Special jigs, fixtures and tools are developed for specific purposes but many operations need dust-free hoods-miniature aseptic rooms located on the working bench. Even when the aseptic hoods or chambers are located in dust free rooms, they may have to be provided with supply of pressurized air in each one of them. The air may be either super cleaned or an inert gas. Further these hoods have to be independently illuminated.
There are many several important factors to consider when called upon compounding a sterile ophthalmic preparation. Eyes are very sensitive to heat, light, drugs and chemicals. In many cases, the drugs involved have a narrow therapeutic range and even small errors when introduced have the potential to cause irreversible damage to the eye or loss of the eye sight. The following considerations are recommended whenever preparing such a product.
1. Ensure concentration is within the acceptable range or not before dispensing of the product.
2. Sterility of the final product is a must, strictly handled in aseptic area.
3. The pH of the final product must be within an acceptable range.
4. Stability of the final product must be known, as well as the recommended storage requirements.
5. Suitable knowledge of potential diluents or vehicles is required in order to ensure proper tonicity, viscosity, or dissolution of the final product.
6. Proper documentation of each step is an important consideration to reduce error.
7. If the preparation of a product requires the breaking of an ampoule or the reconstitution of a powder, it is recommended that the final product be made in sterile water for injection and free from particulate matter.
8. The preparation of intra-occular products requires the use of preservative-free ingredients. Many preservatives have been found to be toxic to the inner ocular tissues.
9. Finally, before dispensing the finished product, always indicate the storage requirements, concentrations of ingredients, and the expected expiration date.
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