Tablet Coating Equipment

Difference Between Coated Tablets and Uncoated Tablets

Depending on the application, coated and uncoated tablets have their own advantages and disadvantages. Since coated tablets have an additional coating process, manufacturing costs are higher than uncoated tablets. In applications where the medication must be released slowly or move further beyond the stomach to the intestines, a tablet with an enteric coating becomes essential. Its purpose is to shield the tablet from rapid degradation caused by stomach acid exposure.

Uncoated tablets have exposed active ingredients and excipients, which allow the medication to break down quickly and be absorbed easily by the body, which is suitable for applications that require immediate action. Uncoated tablets are also cheaper to manufacture since they do not have an additional coating process. Coating alters tablet properties like taste, odor, texture, and how the tablet is dissolved in the patient’s body. Enteric-coated tablets allow delayed drug release for the medication to get past the stomach acid and dissolve where intended, making the medicine more effective.

Different Types of Coated Tablets

In most cases, pharmaceutical tablets don’t taste well but are necessary for medicinal or supplementary purposes like vitamins for kids. Sugar-coated tablets are a good option to improve the taste and aroma of the tablet, making it easy for patients, especially children, to take. Film-coated tablets reign as the predominant tablet variety in the pharmaceutical industry, boasting a plethora of benefits. These advantages include masking the taste and odor, allowing the application of colors for easy product identification, and maintaining a stable tablet with longer life and better resistance from exposure to light and moisture.

In cases where two incompatible active pharmaceutical ingredients need to be combined in a single tablet, also known as a combination tablet, compression coating or dry coating method is used. This method allows one active ingredient to be contained in the tablet core while the other in the coating. Sustained-release or extended-release tablets use polymer coating similar to an enteric coating that slowly dissolves over a sustained period in the body, eliminating abrupt bursts of drug release.

Film coating solutions for pharmaceutical tablets

Film-coated tablets are the pharmaceutical industry's prevailing choice for a wide array of solid oral medications, primarily due to their numerous advantages. Like other coated tablets, they enhance stability and visual appeal while concurrently concealing taste and facilitating controlled drug release, all are made possible through the selection of purpose-specific film-coating materials.

The film coating process starts with the tablets loaded into the coating pan, forming a tablet bed. The tablet bed tumbles slowly while a controlled airflow is introduced. When the desired temperature is reached, the coating solution is sprayed onto the bed until the tablets are fully coated. The controlled temperature and airflow operate simultaneously to allow the tablets to quickly dry and form a thin film all over the tablet. Various coating solutions are available depending on your product application.

Organic film coating is a solution made up of polymers, colorants, and excipients dissolved in organic solvents. Polymers like ethyl cellulose and hydroxypropyl methylcellulose (HPMC) are widely used in film coating to form flexible films that adhere strongly to the tablet’s surfaces while being highly soluble in organic solvents. Another coating option is aqueous film coating, which employs water as the coating solvent. This choice is considered safer due to its lower flammability and reduced toxicity, making it both cost-effective and environmentally friendly when contrasted with organic solvents.

Enteric coating for modified-release tablets

Enteric-coated tablets are tablets coated with pH-sensitive polymers such as acrylate polymers and hydroxypropyl methylcellulose phthalate (HPMCP). These polymers prevent the tablet core from disintegrating in the stomach, where pH levels are acidic. The coating is only soluble when it reaches the small intestines, with basic pH levels. Examples of common polymers used for enteric coating formulations are Cellulose acetate phthalate (CAP), which has a high hydrolysis potential when exposed to high temperature and humidity, and Hydroxypropyl methylcellulose acetate succinate (HPMCAS), which has a low hydrolysis potential under elevated temperature and humidity. Although both are used for the same purpose, we must consider the compatibility of the tablet core’s chemical composition with the enteric coating applied.

Coating in laboratory scale to industrial scale

Tablet coating between industrial scale and small-scale production are similar in process but differ in loading capacity and equipment performance.

Other notable differences between industrial scale and laboratory scale systems are the pan perforations where controlled air passes; the ideal drum spin rate for providing adequate mixing without breaking the tablets; inlet air flow rate for drying; the number of spray nozzles and their volume flow rate; the number of baffles to avoid twinning of tablets; and the ideal temperature and humidity for during operation to achieve uniformity. Both approaches are essential in the pharmaceutical industry, catering to diverse needs, from mass production to customized drug delivery systems.

Tablet Coating Technologies

In the pharmaceutical industry, several prevalent coating technologies include sugar coating, film coating, compression coating, and enteric coating. Sugar coating, in particular, encompasses a multi-step process that includes sealing, subcoating, syrup coating, coloring, and polishing. This method results in a thicker coating layer due to the application of multiple coating layers.

Film coating uses a rotating pan with baffles and an efficient spraying system for the coating solution. A controlled airflow and temperature allow the film coating to dry quickly. Enteric coating follows the same principle as film coating but utilizes enteric coating polymers, which are resistant to stomach acid to coat the external surfaces of the tablet core. At basic pH levels, the enteric coating disintegrates and exposes the tablet core.

 

Testing for quality and regulation compliance

Based on the International Council for Harmonisation (ICH) guidelines, organic solvents must be avoided in the formulation of pharmaceutical dosage forms due to safety issues regarding health and environmental risks. Because of this, manufacturers are shifting to the aqueous film coating method, which uses water-based coating solutions that are less toxic to health and the environment. Coated tablets' assessment and quality testing involve a comprehensive set of evaluations.

These encompass visual appearance inspections, disintegration tests where tablets are submerged in 37°C water to replicate stomach conditions with recorded disintegration times, dissolution tests, and scrutiny of drug content. Advanced analytical instruments like near-infrared and Raman spectroscopy are employed for precision, uniformity of content, and weight assessments. Furthermore, tablets undergo hardness assessments and friability tests, which are weighed before and after being subjected to a rotating drum to determine any weight loss percentage due to chipping or breakage. Additional evaluations include adhesion tests and assessments of water vapor stability.

Tablet coating process challanges

It is necessary for manufacturers to understand the properties of various excipients and the formulation of the coating materials to select the most compatible coating application for the tablet core. Coating adhesion problems may require changes to the polymer mixtures for coating by using Hypromellose and copovidone as the primary polymer. Other challenges include the blistering of tablets, where the film coating detaches from the core due to high-temperature application during the drying process. The drying process must apply mild drying conditions, such as moderate temperatures, during the coating process. Chipping and erosion can happen for reasons like the tablet profile has sharp edges or due to alterations to the coating process like slow pan rotation, low spray rate, or even poor coating formulation. By adjusting the proportion of the plasticizer or selecting a polymer with high molecular weight for the coating solution, the hardness of the coating can be increased. Manufacturers must understand the limits and the specific ideal conditions necessary for coating their products to minimize defects and waste in production.