Manufacture of Sterile Products

MANUFACTURE  OF  STERILE  PRODUCTS       

For production purposes an important distinction exists between sterile products which have been terminally sterilized (Figure 23.2a) and those which have not. Terminal sterilization involves the product being sealed in its container and then sterilized, usually by heat, but ionizing radiation or, less commonly, ethylene oxide may be employed. Such a product must be manufactured in a clean area. A product which cannot be terminally sterilized is prepared aseptically (Figure 23.2b) from previously sterilized materials or by sterile filtration; in either case, aseptic filling is a poststerilization step. Strict aseptic conditions are required throughout.

Vaccines, consisting of dead microorganisms, microbial extracts or inactivated viruses may be filled in the same premises as other sterile medicinal products, so the completeness of killing or removal of live organisms must be validated before processing. Separate premises are needed for the filling of live or attenuated vaccines and for the preparation of other products derived from live organisms. Non-sterile products and sterile products must not be processed in the same area.

A)   Clean And Aseptic Areas: General Requirements

                      i)  Design of premises

Sterile production should be carried out in a purposebuilt unit separated from other manufacturing areas and thoroughfares. The unit should be designed to encourage separation of each stage of production but should ensure a safe and organized workflow. A plan of such a facility is shown in Figure 23.3. Sterilized products held in quarantine pending sterility test results  must be kept separate from those awaiting sterilization.

                    ii) Internal Surfaces, fittings and floors

Particulate, as well as microbial, contamination must be prevented. To this end all surfaces must be smooth and impervious in order to: (1) prevent accumulation of dust or other particulate matter; and (2) permit easily repeated cleaning and disinfection. Smooth rounded coving should be used where the wall meets the floor and the ceiling.

Suitable flooring may be provided by welded sheets of PVC; cracks and open joints which might harbour dirt and microorganisms must be avoided. The preferred surfaces for walls are plastic, epoxy-coated plaster, plastic fibreglass or glass-reinforced polyester. Often the final finish for the floor, wall and ceiling is achieved using continuous welded PVC sheeting. False ceilings should be adequately sealed to prevent contamination from the space above. Use should be made of well-sealed glass panels, especially in dividing walls, to ensure good visibility and allow satisfactory supervision. Doors and windows should be flush with the walls. Windows should not be openable.

Internal fittings such as cupboards, drawers and shelves should be kept to a minimum. They must be sited where they do not interfere with the laminar flow of the filtered air supply. Stainless steel or laminated plastic are the preferred materials for such fittings. Stainless steel trolleys may be used to transport equipment and materials within the clean and aseptic areas but must remain confined to their respective units. Equipment must be designed so that it may be easily cleaned and sterilized or disinfected.

                      iii)  Services

Clean and aseptic areas must be adequately illuminated; lights are best housed in translucent panels set in a false ceiling. Electrical switches and sockets must be flush with the wall or fitted outside. When required, gases should be pumped in from outside the unit. Pipes and ducts, if they must be brought into the clean area, must be sealed through the walls. Additionally, in order to prevent dust accumulation, pipes and ducts must be boxed in or readily cleanable. Alternatively, they may be sited above false ceilings.

Sinks should be of stainless steel with no overflow, and water must be of at least potable quality. Wherever possible, drains should be avoided. If installed they must be fitted with effective, readily cleanable traps and with air breaks to prevent backflow. Any floor channels should be open, shallow and cleanable and connected to drains outside the area; they should be monitored microbiologically. Sinks and drains should be excluded from aseptic areas except where radiopharmaceuticals are being processed when sinks are a requirement.

                 iv)  Air Supply

Areas for sterile manufacture are classified according to the required characteristics of the environment. Each operation requires an appropriate level of microbial and particulate cleanliness; four grades are specified in The Rules and Guidance for Pharmaceutical Manufacturers and Distributors (2007). Environmental quality is substantially influenced by the air supplied to the manufacturing environment. The grades of air required for specific manufacturing activities are listed in Table 23.3.

Filtered air  is used to achieve the necessary standards; this should be maintained at positive pressure throughout a clean or aseptic area, with the highest pressure in the most critical rooms (aseptic or clean filling rooms) and a progressive reduction through the preparation and changing rooms (Figure 23.4); a minimum pressure differential of 10 kPa is normally required between each class of room. A minimum of 20 changes of air per hour is usual in clean and aseptic rooms. The air inlet points should be situated in or near the ceiling, with the final filters placed as close as possible to the point of input to the room. Equipment or furnishings must be sited so as not to interfere with laminar flow.

The greatest risk of contamination of a product comes from its immediate environment. Additional protection is needed both in the filling area of the cleanroom and in the aseptic suite. This can be provided by a workstation supplied with a unidirectional flow of filtered sterile air. This is known as a laminar flow cabinet. Displacement of air may be vertical or horizontal with a typical homogeneous air flow of 0.45 m/s at the working position. Consequently airborne contamination is not added to the work space, and any generated by manipulation is swept away by the laminar air currents. A fuller description of high efficiency particulate air (HEPA) filters in laminar flow cabinets is given by Gardner and Peel (1998).

The efficacy of the filters through which the air is passed should be monitored at predetermined intervals. Air quality may be monitored for bacteria and fungi by slit sampler or settle plate. Particles are measured using a discrete airborne particle counter. The latest edition of The Rules and Guidance for Pharmaceutical Manufacturers and Distributors (2007) states that particles must be monitored continuously in a grade A area and recommends it for grade B areas. It should be noted that grade A air is not the purest that can be obtained; four even cleaner grades are used in the electronics industry (ISO14644-1).

               v)             Clothing

Clothing worn in a clean area must be of non-shedding fibres; polyester is a suitable fabric. Airborne contamination, both microbial and particulate, is reduced when trouser suits, close-fitting at the neck, wrists and ankles, are worn. Clean suits should be provided once a day, but fresh headwear, overshoes and powder-free gloves are necessary for each working session. Special laundering facilities are desirable.

             vi)              Changing facilities

Entry to a clean or aseptic area should be through a changing room fitted with interlocking doors; this design acts as an airlock to prevent influx of air from the outside. This route is for personnel only, not for the transfer of materials and equipment. Staff entering the changing room should already be clad in the standard factory or hospital protective clothing. For entry into a clean area, passage through the changing room should be from a ‘black’ to a ‘grey’ area, via a dividing step-over sill (Figure 23.4). Movement through these areas and finally into the cleanroom is permitted only when observing a strict protocol, whereby outer garments are removed in the ‘black’ area and cleanroom trouser suits donned in the ‘grey’ area. Only after hand-washing in a sink fitted with elbowor foot-operated taps may the operator enter the cleanroom.

          vii)          Cleaning and disinfection

A strict, validated disinfection policy is necessary if microbial contamination is to be kept to a minimum. Cleaning agents used include alkaline detergents and ionic and non-ionic surfactants. A wide range of chemical disinfectants is available. Clear, soluble phenolics are commonly used for interior services and fittings. Disinfectants for working surfaces are alcohols (70% ethanol or isopropanol) or, less commonly, chlorine-based agents such as hypochlorites. Skin may be disinfected with cationic detergents such as cetrimide or chlorhexidine, usually formulated with 70% alcohol to avoid the need for rinsing. Gloved hands may be disinfected with these detergents or 70% alcohol. The former have the advantage of offering residual activity. Rotation of different disinfectants reduces the risk of the emergence of resistant strains, but such rotation should be validated. In-use dilutions must not be used unless sterilized. Disinfectants and detergents for use in grade A/B areas must be sterile prior to use and formulated with water for injections. Modern sprays are fitted with devices to prevent air being sucked back, extending the life of the disinfectant. Smooth polished surfaces are more readily cleaned. Floors and horizontal surfaces should be cleaned and disinfected daily, walls and ceilings as often as required, but the interval should not exceed 1 month. Regular microbiological monitoring should be carried out to determine the efficacy of disinfection procedures. Records must be kept and immediate remedial action taken should normal levels for that area be exceeded.

          viii)        Operation

The number of persons involved in sterile manufacture should be kept to a minimum to avoid the inevitable turbulence and shedding of particles and organisms associated with the operatives. All operations should be undertaken in a controlled and methodical manner as excessive activity may increase turbulence and particle shedding.

Containers made from fibrous materials such as paper, cardboard and sacking are generally heavily contaminated (especially with moulds and bacterial spores) and should not be taken into clean areas. Ingredients which must be brought into clean areas must first be transferred to suitable metal or plastic containers. Containers and closures for terminally sterilized products must be thoroughly cleaned before use and should undergo a final washing and rinsing process in apyrogenic distilled water (which has been passed through a bacteria-proof membrane filter) immediately prior to filling. Containers and closures for use in aseptic manufacture must, in addition, be sterilized after washing and rinsing in preparation for aseptic filling.