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Used in the pharmaceutical industry to produce tablets and capsules, among others, pharmaceutical granules are made to enhance the uniformity and flow of powder, increase the density of the blend and reduce dust and, therefore, toxic exposure. The choice of the granulation process, whether it is wet, dry, or direct compression, as well as the selection of appropriate pharmaceutical granulation equipment, depends on the specific drug being formulated.

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Pre-granulation and formulation of granules

Granulation is a commonly used technique for particle enlargement in pharmaceutical manufacturing – mixtures are agglomerated into semi-permanent aggregates by mixing active pharmaceutical ingredients, known as APIs and excipients. The latter has numerous functions, for instance, those that promote binding and improve tablet hardness, such as binders and disintegrants, or enhancing patient acceptance with flavors. Other excipients, such as hydrophilic polymers and wetting agents, optimize or modify drug release, while antioxidants enhance stability.

The granulation process can be divided into two main types: wet and dry granulation. Dry granulation is used when ingredients are moisture or heat-reactive. It is an efficient process due to simple equipment and minimum processing required. On the other hand, wet granulation is a complex process with various pharmaceutical granulation equipment and steps. Although more costly, it is also a more widely used process, especially useful in processing soluble low-dose drugs.

Pharmaceutical granulation equipment for wet, dry, and direct compression processes

As the names imply, the process of wet granulation utilizes a liquid, while dry granulation requires no liquid. The first step in the dry granulation process is weighing all the ingredients which are then mixed until they form a uniform powder. In a process called slugging, the mixture is compressed into pallets and broken into smaller pieces using a hammer mill. To achieve a uniform blend, excipients such as lubricants and disintegrants are added.

The wet granulation technique uses the same preparatory and finishing steps with the addition of wet massing, wet screening, and drying. Mass wetting is a process during which a granulation agent is added to the mixture until it disperses uniformly. The slurry is then sieved into granules and dried. This method offers a higher level of uniformity and speeds up the dissolution process. In the direct compression process, the blend is added directly into a tablet compression machine that produces tablets.

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Granulation process for tablets and capsules

Once the granulation process is finished, granules are either pressed into tablets or filled into capsules, depending on their properties. A tablet is a solid form of an active ingredient in which it is possible to pack more material than with capsules. As the tablet presses can manufacture hundreds of thousands of tablets per minute, the formulation must be designed to flow consistently and fill volumetrically to achieve consistency among tablets. Some key excipients in tablet production are lubricants to prevent the granules from sticking, fillers to bulk up tablets, and disintegrants to help the tablet break up upon consumption.

On the other hand, capsules are filled with granulated powder with uniform particle sizes that flow freely; therefore good flow properties are essential. For efficiency and accuracy, granules are filled into hard gelatine capsules with the help of an automated capsule-filler machine.

Innovating high-shear mixers in the granulation industry

Although high-shear mixers have stood the test of time, being used in granulation processes for over six decades, there have been some recent innovations in the pharmaceutical industry. Namely, high-shear mixers can work under a vacuum and dry the wet mass within itself or are provided with fluid bed processors so that all the stages are carried out within the same mainframe equipment. These mixers have the capability to handle very fine particle coating of 75 to 100 microns. The popularity of such mixers lies in their simplicity and the fact that they are used as one-stage one-step equipment from the start till the loading of the granules atop the compression table.

What is the most environmentally sustainable granulation process?

Representing one of the most carbon-intensive industries due to the complex chemistry of APIs, the pharmaceutical industry has put efforts into improving the environmental sustainability of its manufacturing process. In granulation processes, the environmental impact of production is ruled by process-level energy usage – a more complex process means more impact on the environment. Therefore, a shorter process, such as direct compression, which uses more energy, is a more environmentally friendly choice. However, this applies to drugs with good flowability, as those with poor flowability require either pre-compaction treatment, increased excipients’ proportion in the tablets, or using excipients with unfavorable sustainability profiles. Furthermore, organic solvent-free processes, such as using lipid excipients, are an excellent alternative for making the granulation process greener.