Some like it hot
Pharmaceuticals are often administered via the oral route - the cheapest, simplest and safest approach. However, many active pharmaceutical ingredients (APIs) need to be effectively coated to ensure stability, efficacy and the desired API release profile.
Commonly, pharmaceutical coating involves dissolving the API and/or excipients in a solvent and using the mixture to coat a seed particle via a fluid-bed process. While well established, solvent-based coating suffers from several important drawbacks. Firstly, the coated particles must be dried, which takes considerable time and heat energy, particularly when using water. In some cases, the constituents cannot be dissolved in water and organic solvents such as alcohols, ketones and ethers must be used instead. These are frequently toxic, flammable and expensive, making them less than ideal for use in pharmaceutical coating.
Better coating methods
Hot melt coating (HMC) is becoming a go-to technique for companies looking to avoid the drawbacks of solvent-based coating, while simultaneously gaining greater control over taste characteristics and API release parameters.
When carrying out HMC, the seed API particles are suspended in a fluid bed coater, while the excipients are heated in a suitable external container until they are molten. The molten mix is then transported via a heated tubing system into the fluid bed coater and sprayed directly onto the seed particles using a heated nozzle.
HMC offers many advantages over conventional solvent-based coating technologies. The need for solvents is eliminated, while the process is also faster than solvent-based methods. In addition, HMC does not suffer from curing or sintering effects and there is very little risk of forming unwanted products such as agglomerates. The lipid coat also increases the overall hydrophobicity of the final product, inhibiting the uptake of moisture from the environment and further improving stability.
While formulation development requires specific expertise and coating set-ups, the unique conditions required for each product can also prove advantageous, as they provide a means of protecting intellectual property. Pharmaceutical companies can therefore employ HMC to revitalise ageing products and/or create new formulations that are more difficult for competitors to copy.
Both novel and traditional dosage forms can benefit from HMC, as it enables formulators to develop fast- and delayed-release profiles with optimal stability characteristics. HMC parameters can be optimized to create both immediate and extended release forms – including both types within a single dose if required. This can be used to simplify complex dosage regimens – which have traditionally required multiple tablets taken throughout the day – down to one or two doses per day, increasing patient compliance and treatment effectiveness.
HMC is also especially powerful for innovative dosage forms such as orally disintegrating granules (ODGs), a member of a new class of pharmaceutical dosage forms known as user-friendly dosage forms, which have been specifically designed with all the needs of the patient in mind. ODGs can be applied directly into the mouth and do not require any water, making them a much more convenient option for today’s busy consumer. As they start to dissolve in the mouth, they are also easier for patients to take, making them ideal for people who have difficulties swallowing solid tablets. However, as ODGs tend to spend more time in the mouth, they are tasted more thoroughly than solid tablets or capsules. This means that an effective coating is necessary to mask the unpleasant taste inherent to most APIs, as well as to create a good mouth feel and protect the API from being released too early. HMC is an effective option for creating ODGs with the necessary characteristics.
HMC can also be used for solid tablets. In this case, the HMC-coated particles are blended with further excipients and compressed to form a tablet called a multiple unit pellet system (MUPS). The main reason to select HMC for the constituents of solid tablets is to manipulate the release profile of the API and improve the stability of particularly sensitive APIs. Furthermore, tablets composed of uncoated constituent particles tend to absorb saliva and can feel unpleasant in the mouth. MUPS tablets created using HMC coated particles avoid these problems and are therefore easier for patients to swallow. Hard gelatin capsules (HGCs) with altered API release profiles can also be created using HMC, without compromising on API stability.
HMC offers significant advantages in comparison to conventional solvent-based pharmaceutical coatings and is frequently both cheaper and faster than traditional approaches. It can be used to coat constituents of traditional solid oral dosage forms such as capsules and tablets, as well as user-friendly forms, enabling the formulation and production of dosage forms with fast and extended release. The technique is now commercially available and ready for utilization by pharmaceutical companies interested in formulating new or existing medicines with specific API release, taste and user-friendly characteristics.