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Pharma solid dosage form preparation methods

P Mandal
Wednesday, May 18, 2022, 08:00 Hrs  [IST]

A pharmaceutical tablet is defined as a solid dosage form containing drug material normally with suitable diluents and prepared either by compression or molding methods.
Drug formulation and design can be described as the process where by the formulator ensures that the correct amount of the drug in the right form is delivered at or over the proper time at the appropriate rate and in the desired location, while having its chemical integrity protected to that point. Latest concepts and regulations focus on bioavailability, bioequivalence, and validation etc. impact formulation designing and production.
The design and production of pharmaceutical tablets is a complex multi-stage process whereby formulation scientists ensure that the correct amount of drug material in the right form is delivered at the appropriate time at the proper rate and in the desired location with its chemical integrity protected to that point.
However, most drug materials do not possess the needed properties which give satisfactory flow from the hopper to the die cavity of tablet presses. As a result, they are subjected to pre-treatment either alone or in combination with suitable excipients to form free-flowing granules that lend themselves to tableting. Tablets are commonly manufactured by wet granulation, dry granulation or direct compression methods.
As innovative technology is advancing in every industrial sector, the way we operate our equipment is always changing. With new advances in technology come a bigger focus on how it can improve production volume, reduce downtime and safety hazards, and streamline costs in a variety of applications.

Technology advances
As technology advances and applications in manufacturing and processing become more available and accurate, many experts believe we are in a new industrial revolution.

Till the recent past, majority of the pharmaceutical manufacturing companies relied on a process known as batch manufacturing to supply their products to the public. However, with the proliferation and sustained interest in certain drug products, continuous pharmaceutical production has gained more prominence.
While both batch processing and continuous flow manufacturing are great tools within the pharmaceutical sector, both have their ups and downs depending on the needs of pharmaceutical manufacturers and consumers.
Pharmaceutical tablets remain famous as a dosage form because of the advantages afforded, both to the pharmaceutical company - e.g., simplicity and economy of the preparation, stability, and convenience in packing, shipping, dispensing. Because of their composition, method of production or intended use, tablets present a variety of characteristics and consequently there are many categories of tablets.
Wet granulation
The method of wet granulation is the most widely used preparation process of tablet. In this method the powders are bound by suitable binder by adhesion. The binder is included by diluting with suitable solvent prior to addition to the blended powders to form wet granules which in turn are dried suitably to expel the solvent forming dried granules.
The surface tension forces and capillary pressure are primarily responsible for initial granules formation, the main advantage being it meets all the requirements for tablet formation.
Wet granulation process consists of dry mixing; wet mixing; milling of the wetted mass; drying; milling of the dried mass and finally blending.
Wet granulation is a widely used method for the production of compressed tablet. It is essentially a process of size enlargement involving several steps and the use of an adhesive substance known as binder. The granules produced using this method of meeting all granulation has a greater probability of the physical requirements for tablet formation.
The process of wet granulation consists of a number of steps which include: Weighing and blending; Preparing wet granulate by adding the binder solution; Screening the damp mass into pellets; Drying the granulation in thermostatically controlled overs;
Dry screening; Mixing with other ingredients; and Tableting in which the table is fed into the die and then it is compressed.    
Dry granulation
The main difference between dry granulation and wet granulation is that dry granulation is the process of forming granules without using any liquid solution whereas wet granulation is the process of forming granules by adding a granulating liquid.
Dry granulation process is used to form granules without using a liquid solution. This type of process is recommended for products, which are sensitive to moister and heat. Forming granules without moisture requires compacting and densifying the powders.
Dry granulation can be done on a tablet press using slugging tooling. On large-scale roller compactor commonly referred to as a chilsonator. The compacted mass is called slugs and the process is known as slugging. The slugs are then screened to produce a granular form of tablet materials, which have the good flow properties then original powder mixture.
The main advantage of dry granulation is it needs less equipment and eradicates the addition of moisture and the application of heat as found in wet massing and drying steps of the wet granulation method.
Manufacture of oral solid dosage forms
The manufacture of oral solid dosage forms such as tablets is a complex multi-stage process under which the starting materials change their physical characteristics a number of times before the final dosage form is produced.
Tablets have been made by granulation, a process that imparts two primary requisites to formulate: compatibility and fluidity. Both wet granulation and dry granulation are used. Regardless of whether tablets are made by direct compression or granulation, the first step, milling and mixing, is the same; subsequent step differ.
Numerous unit processes are involved in making tablets, including particle size reduction and sizing, blending, granulation, drying, compaction, and coating. Various factors associated with these processes can seriously affect content uniformity, bioavailability or stability.
Tablets formation process consist of a series of steps such as weighing, milling, mixing, granulation, drying, compaction, coating and packaging. Regardless of the method used the unit processes - weighing, milling and mixing are the same.
Primary goals of tablet manufacturing process are: to formulate tablets that are strong and hard to withstand mechanical shock encountered during manufacturing, packing, shipping, dispensing and use; to formulate tablets that are uniform in weight and in drug content; to formulate tablets that are bioavailable according to indication needs; to formulate tablets that are chemically and physically stable over a long period of time; to formulate tablets that have elegant product identity which is free from any tablet defects.
Some categories of the tablets for oral use are: soluble tablets; oral lyophilisates; gastro-resistant tablets; uncoated tablets; coated tablets; modified-release tablets; orodispersible tablets; effervescent tablets; dispersible tablets; chewable tablets.
Continuous manufacturing
Nowadays more pharmaceutical manufacturers are turning to continuous manufacturing processing for developmental drugs in their pipeline.  Traditional pharmaceutical batch processing sees the various components of a drug brought together through a step-by-step process. As the materials go from step-to-step, the current batch must finish before a subsequent batch can be processed.

There may be upwards of six or seven steps in the process that are completed within six or seven pieces of equipment before a product is getting completed. Continuous pharmaceutical manufacturing process sees a drug taken from its base ingredients to the final product with no need to stop during production. This means there is no need to cease the operation of the equipment and no down time as the product is created.
Essentially, batch processing must stop from step to step throughout creation while the continuous process creates a product with no need to stop until the product is complete. Both processes provide pros and cons to the manufacturer, and either one is a perfectly sound way to produce a great final product, depending on your needs.

Advantages of batch production is that the set-up costs are initially less expensive. Also, each batch is more easily tailored to be unique. Lastly, there are certain products that require batch manufacturing due to their composition. Using batch production, pharmaceutical manufacturing companies can manufacture specific amounts of a certain product and then adjust their manufacturing priorities according to the demands of the markets.  
Pharmaceuticals are a delivery system compounded with the active substance and a number of ingredients to facilitate ease of administration and manufacture. Generally, the dosage forms are solid, liquid, injectable solution, nasal spray, cream, or ointment, collectively referred to as conventional dosage forms.
Novel pharmaceutical dosage forms consists of a wide range of formulation delivery platforms such as tablets, capsules, cachets, sustained release dosage forms, parenteral dosage forms, transdermal dosage forms, metered dose inhalants, solutions, emulsions, and suspension.
With more products requiring complex manufacturing processes, pharmaceutical developers are also struggling to find the required technical set-up which is also manageable from a cost standpoint.
In pharma product design stage, often there is more than one delivery technology, formulation approach, or production method that is suitable for developing a viable product with predetermined quality and performance for a specific active pharmaceutical ingredient.
Rational selection of a dosage form and associated drug delivery technology, formulation, and manufacturing process needs to be based on a concurrent and integrated evaluation of a multitude of factors discussed in the previous sections, such as active pharmaceutical ingredient characteristics, material properties, processing operations and their interaction, variations, process robustness and efficiency.
Pharmaceutical solid dosage form development often involves the characterization of raw materials going into the manufacturing of the active pharmaceutical ingredient so that the correct form for development can be selected; characterized the excipient and intermediates in dosage form manufacturing.

Pharmaceutical manufacturing companies across the globe are optimistic and hoping the emerging markets will play an important role in future days. The quick development of the emerging markets, the rise in generic drugs and advancements in the areas of drug development and production processes will influence the pharmaceutical landscape.
Indian pharmaceutical manufacturing companies’ ability in biology, skill in chemistry and genetics coupled with low-cost clinical trial operability are making India an attractive location for new drug molecule discovery and outsourced research and development for key global pharmaceutical players.
(The author is a practicing chemical engineer)


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