The processes required for preparing sterile products constitute a series of events initiated with the procurement of approved raw materials (drugs, excipients, vehicles, etc.) and primary packaging components (containers, closures, etc.) and ending with the sterile product sealed in its dispensing package. Each step in the process must be controlled very carefully, so the product has its required quality.
Cleaning Containers and equipment: Containers and equipment coming in contact with parenteral preparations must be cleaned meticulously. It should be obvious that even new, unused containers and equipment are contaminated with such debris as dust, fibers, chemical films, and other materials arising from such sources as the atmosphere, cartons, the manufacturing process, and human hands. Residues from previous use must be removed from used equipment, before it is suitable for reuse. Equipment should be reserved exclusively for use only with parenteral preparations and, where conditions dictate, only for one product to reduce the risk of contamination. For many operations, particularly with biologic and biotechnology products, equipment is dedicated for only one product. A variety of machines are available for cleaning new containers for parenteral products.
Characteristics of machinery – Regardless of the type of cleaning machine selected, certain fundamental characteristics are usually required:
- The liquid or air treatment must be introduced in such a manner that it will strike the bottom of the inside of the inverted container, spread in all directions, and smoothly flow down the walls and out the opening with a sweeping action. The pressure of the jet stream should be such that there is minimal splashing and turbulence inside. Splashing may prevent cleaning all areas, and turbulence may redeposit loosened debris. Therefore, direct introduction of the jet stream within the container with control of its flow is required.
- The container must receive a concurrent outside rinse.
- The cycle of treatment should provide a planned sequence, alternating very hot and cool treatments. The final treatment should be an effective rinse with WFI.
- All metal parts coming in contact with the containers and with the treatments should be constructed of stainless steel or some other non corroding and non-contaminating material.
Treatment cycle – The cycle of treatments to be employed varies with the condition of the containers to be cleaned. In general, loose debris can be removed by vigorous rinsing with water. Detergents are rarely used for new containers, due to the risk of leaving detergent residues. However, a thermal-shock sequence in the cycle is usually employed to aid, by expansion and contraction, loosening of debris that may be adhering to the container wall. Sometimes, only an air rinse is used for new containers, if only loose debris is present. In all instances, the final rinse, whether air or WFI, must be ultra clean, so no particulate residues are left by the rinsing agent.
Machinery for Containers – The machinery available for cleaning containers embodies the previously mentioned principles, but varies in the mechanics by which it is accomplished. In one manual loading type, the jet tubes are arranged on arms like the spokes of a wheel, which rotate around a center post through which the treatments are introduced. An operator places the unclean containers on the jet tubes, as they pass the loading point, and removes the clean containers as they complete one rotation. The vials are fed into the rotary rinser in the foreground, transferred automatically to the covered sterilizing tunnel in the center, conveyed through the wall in the background, and discharged into the filling clean room.
Handling after Cleaning – The wet, clean containers must be handled in such a way that contamination is not reintroduced. A wet surface will collect contaminants much more readily than a dry surface will. For this reason, wet, rinsed containers must be protected (e.g., by a laminar flow of clean air until covered, within a stainless steel box, or within a sterilizing tunnel). In addition, microorganisms are more likely to grow in the presence of moisture. Therefore, wet, clean containers should be dry-heat sterilized, as soon as possible after washing. Doubling the heating period is also adequate to destroy pyrogens; for example, increasing the dwell time at 250° from 1 to 2 hours, however, the actual time temperature conditions required must be validated. The clean, wet containers are protected by filtered, laminar-flow air from the rinser, through the tunnel, and until they are delivered to the filling line.
Closures – The rough, elastic, and convoluted surface of rubber closures renders them difficult to clean. In addition, any residue of lubricant from molding or surface ‘bloom’ of inorganic constituents must be removed. The normal procedure calls for gentle agitation in a hot solution of a mild water softener or detergent. The closures are removed from the solution and rinsed several times, or continuously for a prolonged period, with filtered WFI. The rinsing is done in a manner that flushes away loosened debris. The wet closures are carefully protected from environmental contamination, sterilized, usually by steam sterilization (autoclaving), and stored in closed containers, until ready for use. This cleaning and sterilizing process must also be validated with respect to rendering the closures free from pyrogens. The equipment used for washing large numbers of closures is usually an agitator or horizontal basket-type automatic washing machine.
Equipment – All equipment should be disassembled as much as possible to provide access to internal structures. Surfaces should be scrubbed thoroughly with a stiff brush, using an effective detergent and paying particular attention to joints, crevices, screw threads, and other structures where debris is apt to collect. Exposure to a stream of clean steam aids in dislodging residues from the walls of stationary tanks, spigots, pipes, and similar structures. Thorough rinsing with distilled water should follow the cleaning steps.
- A master formula should be developed and be on file. Each batch formula sheet should be prepared from the master and confirmed for accuracy. All measurements of quantities should be made as accurately as possible and checked by a second qualified person.
- Care must be taken that equipment is not wet enough to dilute the product significantly or, in the case of anhydrous products, to cause a physical incompatibility.
- The order of mixing of ingredients may affect the product significantly, particularly those of large volume, where attaining homogeneity requires considerable mixing time.
- Parenteral dispersions, including colloids, emulsions, and suspensions, provide particular problems. In addition to the problems of achieving and maintaining proper reduction in particle size under aseptic conditions, the dispersion must be kept in a uniform state of suspension throughout the preparative, transfer, and subdividing operations.
- Biopharmaceuticals are usually extremely sensitive to many environmental and processing conditions exposed to during production, such as temperature, mixing time and speed, order of addition of formulation components, pH adjustment and control, and contact time with various surfaces, such as filters and tubing.
Filtration: After a product has been compounded, it must be filtered, if it is a solution. The primary objective of filtration is to clarify a solution. A further step, removing particulate matter down to 0.2 μm in size, would eliminate micro-organisms and would accomplish cold sterilization. A solution with a high degree of clarity conveys the impression of high quality and purity, desirable characteristics for a parenteral solution. Filters are thought to function by one or, usually, a combination of: 1) sieving or screening, 2) entrapment or impaction, and 3) electrostatic attraction. Membrane filters are used exclusively for parenteral solutions, due to their particle-retention effectiveness, non-shedding property, non-reactivity, and disposable characteristics. Filters are available as flat membranes or pleated into cylinders to increase surface area and, thus, flow rate. Each filter in its holder should be tested for integrity before and after use, particularly, if it is being used to eliminate micro-organisms. This integrity test is performed either as the ‘bubble-point test’ or as the ‘diffusion or forward flow’ test. The bubble point test is commonly used on smaller filters. As the surface area of filters becomes large, diffusion of air through the water-filled pores tends to obscure the bubble point. Therefore, the diffusion test has been developed as an integrity test for filters with large surface areas. A ‘pressure hold test’ can also be applied to large surface area filters. The filter manufacturer will recommend the best integrity test for the filter system in question. Although membrane filters are disposable and, thus, discarded after use, the holders must be cleaned thoroughly between uses. Today, clean, sterile, pretested, disposable assemblies for small, as well as large, volumes of solutions are available commercially.
Filling – During the filling of containers with a product, the most stringent requirements must be exercised to prevent contamination, particularly if the product has been sterilized by filtration and will not be sterilized in the final container. During the filling operation, the product must be transferred from a bulk container or tank and subdivided into dose containers. This operation exposes the sterile product to the environment, equipment, and manipulative technique of the operators, until it can be sealed in the dose container. Therefore, this operation is carried out with a minimum exposure time, even though maximum protection is provided by filling under a blanket of HEPA-filtered laminar-flow air within the aseptic area.
1.Liquid filling – There are three main methods for filling liquids into containers with high accuracy: volumetric filling, time/pressure dosing, and net weight filling. Volumetric filling machines, employing pistons or peristaltic pumps, are most commonly used. When high-speed filling rates are desired but accuracy and precision must be maintained, multiple filling units are often joined in an electronically coordinated machine. When the product is sensitive to metals, a peristaltic-pump filler may be used, because the product comes in contact only with silicone rubber tubing. However, this sacrifices filling accuracy.
Time-pressure (or time-gravity) filling machines are gaining popularity in filling sterile liquids. A product tank is connected to the filling system equipped with a pressure sensor. The sensor continuously measures pressure and transmits values to the PLC system controlling the flow of product from tank to filling manifold. Product flow occurs when tubing is mechanically unpinched and stops when tubing is mechanically pinched. The main advantage of time/pressure filling operations is that these filling apparatuses do not contain mechanical moving parts in the product stream. The product is driven by pressure (usually nitrogen) with no pumping mechanism involved. Thus, especially for proteins that are quite sensitive to shear forces, time/pressure filling is preferable.
The filling of a small number of containers may be accomplished with a hypodermic syringe and needle, the liquid drawn into the syringe and forced through the needle into the container.
2.Solid filling – Sterile solids, such as antibiotics, are more difficult to subdivide evenly into containers than are liquids. The rate of flow of solid material is slow and often irregular. Even though a container with a larger-diameter opening is used to facilitate filling, it is difficult to introduce the solid particles, and the risk of spillage is ever-present. The accuracy of the quantity delivered cannot be controlled, as well as with liquids. Due to these factors, the tolerances permitted for the content of such containers must be relatively large. Some sterile solids are subdivided into containers by individual weighing. A scoop is usually provided to aid in approximating the quantity required, but the quantity filled into the container is finally weighed on a balance. This is a slow process. When the solid is obtainable in a granular form, so it will flow more freely, other methods of filling may be employed. In general, these involve the measurement and delivery of a volume of the granular material that has been calibrated in terms of the weight desired.
Ampoules sealing – Filled containers should be sealed as soon as possible, to prevent the contents from being contaminated by the environment. Ampoules are sealed by melting a portion of the glass neck. Two types of seals are employed normally: tip-seals (bead-seals) or pull-seals.
Tip-seals are made by melting enough glass at the tip of the neck of an ampoule to form a bead and close the opening. These can be made rapidly in a high-temperature gas-oxygen flame. To produce a uniform bead, the ampoule neck must be heated evenly on all sides, such as by burners on opposite sides of stationary ampoules or by rotating the ampoule in a single flame. Care must be taken to properly adjust the flame temperature and the interval of heating to completely close the opening with a bead of glass. Excessive heating results in the expansion of the gases within the ampoule against the soft bead seal, which causes a bubble to form. If the bubble bursts, the ampoule is no longer sealed; if it does not, the wall of the bubble will be thin and fragile. Insufficient heating will leave an open capillary through the center of the bead. An incompletely sealed ampoule is called a ‘leaker’.
Pull-seals are made by heating the neck of the ampoule below the tip, leaving enough of the tip for grasping with forceps or other mechanical devices. The ampoule is rotated in the flame from a single burner. When the glass has softened, the tip is grasped firmly and pulled quickly away from the body of the ampoule, which continues to rotate. The small capillary tube, thus, formed is twisted closed. Pull-sealing is slower, but the seals are more secure than tip-sealing. Ampoules having a wide opening must be sealed by pull-sealing.
Vials and bottles sealing – Glass or plastic vials and bottles are sealed by closing the opening with a rubber closure (stopper). This must be accomplished as rapidly as possible after filling and with reasoned care, to prevent contamination of the contents. The large opening makes the introduction of contamination much easier than with ampoules. Therefore, during the critical exposure, the open containers should be protected from the ingress of contamination, preferably with a blanket of HEPA-filtered laminar airflow. To reduce friction, so the closure may slide more easily through a chute and into the container opening, the closure surfaces are halogenated or treated with silicone. Container-closure integrity testing has become a major focus for the industry, due to emphasis by regulatory agencies. Container-closure integrity measures the ability of the seal between the glass or plastic container opening and the rubber closure to remain tight and fit and to resist any ingress of microbial contamination during product shelf life.
Rubber closures are held in place by means of aluminum caps. The caps cover the closure, crimped under the lip of the vial or bottle to hold them in place. The closure cannot be removed without destroying the aluminum cap; it is tamperproof. Therefore, an intact aluminum cap is proof that the closure has not been removed intentionally or unintentionally. Such confirmation is necessary to ensure the integrity of the contents, as to sterility and other aspects of quality.
Sterilization: Whenever possible, the parenteral product should be sterilized, after being sealed in its final container (terminal sterilization) and within as short a time as possible after filling and sealing are completed. Since this usually involves a thermal process, although there is a trend in applying radiation sterilization to finished products, due consideration must be given to the effect of the elevated temperature, upon the stability of the product. Heat-labile products must, therefore, be sterilized by a non-thermal method, usually by filtration through bacteria retaining filters. Subsequently, all operations must be carried out in an aseptic manner, so contamination is not introduced into the filtrate.
- Radiation sterilization, as mentioned, is gaining momentum as an alternative terminal sterilization method.
- Dry-heat sterilization may be employed for a few dry solids not affected adversely by the high temperatures and for the relatively long heating period required. This method is applied most effectively to the sterilization of glassware and metal ware. After sterilization, the equipment will be sterile, dry, and, if the sterilization period is long enough, pyrogen-free.
- Saturated steam under pressure (autoclaving) is the most commonly used and the most effective method for the sterilization of aqueous liquids or substances that can be reached or penetrated by steam.
Freeze-Drying (lyophilization): The process of freeze-drying has taken on greater prominence in the parenteral industry, due to the advent of recombinant DNA technology. Proteins and peptides must be freeze-dried for clinical and commercial use. There are other technologies available to produce sterile dry powder drug products besides freeze-drying, such as sterile crystallization or spray-drying and powder filling. g drug products too unstable to be marketed as solutions. The term ‘lyophilization’ describes a process to produce a product that ‘loves the dry state.’ However, this term does not include the freezing process. Therefore, although lyophilization and freeze-drying are used interchangeably, freeze-drying is a more descriptive term. Equipment used to freeze-dry products are called freeze-dryers or lyophilizers. Freeze-drying, essentially, consists of:
- Freezing stage— Freezing the product solution at a temperature below its eutectic (crystalline) or glass transition temperature.
- Primary drying stage— Removing the solvent (ice) from the product, by evacuating the chamber, usually below 0.1torr (100 μm Hg), and subliming the ice onto a cold, condensing surface at a temperature below that of the product, the condensing surface being within the chamber or in a connecting chamber. During primary drying, the temperature of the product must remain slightly below its critical temperature, called ‘collapse temperature.’ Collapse temperature is best measured by visual observation using a freeze-dry microscope that simulates the freezedrying process. Collapse temperature is similar to the eutectic or glass transition temperature of the product.
- Secondary drying stage— Removing bound water from solute(s) to a level that assures long term stability of the product. This is accomplished by introducing heat to the product under controlled conditions, thereby providing additional energy to the product to remove adsorbed water. The temperature for secondary drying should be as high as possible, without causing any chemical degradation of the active ingredient. For small molecules, the highest secondary drying temperature used is 40°C,whereas for proteins it is no more than 30°C.
Figure 1 – Freeze dryer
Table 1 – Advantages and Disadvantages of freezeDrying and Desirable Characteristics of the finished freeze-Dried Dosage form
|Advantages of Freeze-Dried Products
1. Product is stored in dry state-few stability problems
2. Product is dried without elevated temperatures
3. Good for oxygen and/or air-sensitive drugs
4. Rapid reconstitution time
5. Constituents of the dried material remain homogenously dispersed
6. Product is process in the liquid form
7. Sterility of product can be achieved and maintained
|Disadvantages of Freeze-Dried Products
1. Volatile compounds may be removed by high vacuum
2. Single most expensive unit operation
3. Stability problems associated with individual drugs
4. Some issues associated with sterilization and sterility
assurance of the dryer chamber and aseptic loading of vials into the chamber
|Desired Characteristics of Freeze-Dried Products
• Intact cake
• Sufficient strength
• Uniform color
• Sufficiently dry
• Sufficiently porous
• Free of pyrogens
• Free of particulates
• Chemically stable
Multiple choice questions:
1.Which of the following are characteristics of machinery for cleaning containers and equipment for parenterals?
a)The container must receive a concurrent outside rinse
b)The cycle of treatment should provide a planned sequence, alternating very hot and cool treatments. The final treatment should be an effective rinse with WFI
c)All metal parts coming in contact with the containers and with the treatments should be constructed of stainless steel or some other non corroding and non-contaminating material
d)All of these
2.In general, loose debris can be removed by vigorous rinsing with
d)all of these
3.Detergents are rarely used for new containers, due to the risk of leaving detergent residues.
4.Wet, rinsed containers must be protected using
b)a stainless steel box
c)a sterilizing tunnel
d)all of these
5.The equipment used for washing large numbers of closures is usually
a)agitator washing machine
b)horizontal basket-type automatic washing machine
c)both of these
d)none of these
6.Product preparation includes
a)A master formula
b)Proper order of mixing of ingredients
c)Both of these
d)None of these
7.Parenteral dispersions, including colloids, emulsions, and suspensions, provide particular problems. In addition to the problems of achieving and maintaining proper reduction in particle size under aseptic conditions, the dispersion must be kept in a uniform state of suspension throughout the preparative, transfer, and subdividing operations.
8.Filters are thought to function by
a)sieving or screening
b)entrapment or impaction
d)all of these
9.Which of the following are used exclusively for parenteral solutions?
d)all of these
10.Integrity test performed for membrane filter is/are
c)forward flow test
d)all of these
11.Liquid filling is carried out by
c)net weight filling
d)all of these
12.Ampoules are sealed by
d)all of these
13.An incompletely sealed ampoule is called a
d)none of these
14.Pull-sealing is slower, but the seals are more secure than tip-sealing.
15.Which of the following is not an advantage of Freeze-Dried Products?
a)Product is stored in dry state-few stability problems
b)Product is dried without elevated temperatures
c)Good for oxygen and/or air-sensitive drugs
d)Volatile compounds may be removed by high vacuum
- d)All of these
- d)all of these
- c)both of these
- c)Both of these
- d)all of these
- a)membrane filters
- d)all of these
- d)all of these
- d)all of these
- d)Volatile compounds may be removed by high vacuum
- Remington Essential of Pharmaceutics, 1st edition 2013, page no. 517-526.
- Ansel’s Pharmaceutical Dosage Forms and Drug Delivery Systems, 10th edition, page no. 522-527.