In the pharmaceutical industry, stability is more than a requirement – it’s a commitment. The commitment is that a drug that a patient takes today will still be just as effective months or years later as when it left the production floor.
A key factor in ensuring stability and maintaining shelf life is the tablet coating. Out of many potential candidates for coatings, Hydroxypropyl Methylcellulose (HPMC) has become one of the most notable.
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In this article, we will look at HPMC’s influence on tablet coatings and stability and shelf life, what this means, and any advancements in HPMC E5 that improve production environments and patient outcomes.
Why Tablet Coatings Are Important in the First Place?
Tablet coating might appear to just be an aesthetic layer providing drugs with a neat, professional, and uniform appearance; however, there is a lot more going on.
The covering acts as a barrier against environmental conditions that might in turn affect the active pharmaceutical ingredients (API) from being degraded by contact with moisture, light & oxygen (physical stress).
In some cases, the (API) could lose potency before ingestion, which could mean lower therapeutic effects, or worse, unpredictable results (it is also not limited to solid-state drugs).
In addition to providing advantages of sustainability in maintaining and enhancing the drug delivery space, coating layers can help ease the handling of work in progress and reduce dust during packaging. The coatings can also help control the way drugs are delivered to their site of action in the body.
Why HPMC is a Preferred Coating Material?
HPMC (Hydroxypropyl Methylcellulose) is a semi-synthetic polymer from cellulose, and one of the most versatile and safe materials used in tablets. When HPMC is used as a coating agent, it creates a continuous film around the tablet, uniform in thickness. The finished film has surface appeal, but also provides a stable barrier to environmental conditions.
HPMC is commonly used for several reasons, including:
• Moisture Resistant: Hygroscopic drugs deteriorate quickly when exposed to water.
• Good Adhesion: Coats remain intact during long-term storage and after transport.
• Chemical Stability: HPMC is inert and does not react with most Active Pharmaceutical Ingredients (API).
• Compatibility: Good for all drugs, including those sensitive to light and moisture.
HPMC E5 is also particularly valued for having the best viscosity and film-forming properties, making it easily processed and providing consistent protective measures.
How HPMC Tablet Coatings Protect Stability and Shelf Life?
1. Moisture & Oxygen Barrier
HPMC films decrease the ability of moisture and oxygen to penetrate the coating to reach the drug, which is why this barrier is critical for hygroscopic drugs with APIs that are susceptible to oxidation.
The hydrophobic nature of the HPMC coatings limits available water, minimizing the rate of chemical breakdown of the drug, keeping the drug effective for longer.
2. Light Protection
Some materials are photosensitive, and as a result, these compounds can undergo photochemical transformations once exposed to any light. HPMC, because of its ability to add pigments or opacifiers, can block out selective wavelengths of light, thus protecting light-sensitive APIs from degradation.
3. Mechanical Strength
Tablets will always be subjected to constant handling while on the production line, to the point of dispensing at the pharmacy.
In every step of production, tablets are vibrated and subjected to friction, which can all cause cracks, chips, and abrasions, leading to the core being damaged by the environment; therefore, HPMC coatings will represent a layer of protection for tablets from a mechanical aspect.
4. Controlled release abilities
Another added advantage of applying an HPMC coating is being able to modify fluid uptake in HPMC-coated tablets, allowing the manufacturer to control the release rates of a likewise compound.
By modifying the thickness and the type of HPMC, the Manufacturer could create a tablet with immediate, modified release, or sustained release properties for the delivery of the specified therapeutic compound or products.
Factors Affecting HPMC Coating Performance
Despite HPMC being a robust and effective coating, the overall success of HPMC coating relies upon how the HPMC is applied and stored.
Moisture Control
Although HPMC will generally provide moisture resistance, HPMC can still absorb some water during processing. Therefore, proper drying and storage conditions are required to ensure residual water does not adversely affect the stability of the batches produced.
Plasticizer
Plasticizers such as polyethylene glycol or triacetin are usually used in HPMC coatings to enhance flexibility. The choice and concentration of plasticizers must consider the trade-off defined previously: under plasticized coatings will become brittle, and vice versa, too much plasticizer can migrate into the core, leading to a modification of the stability characteristics of the drug compound.
Coating Thickness
A thin coating may leave a product unprotected, and an excessively thick coating may cause undesirably slow dissolution rates. It is a compromise between finding the right thickness that provides stability and the promised therapeutic performance.
Storage Condition
The temperature and humidity of the storage facility may make a difference in shelf life of some tablets. With an effective HPMC coating, it may be possible to protect a product from prolonged exposure to extremes.
HPMC E5’s Importance In Coating Technology
HPMC E5 is a unique grade of HPMC with the best viscosity to processability traits.
Why Formulators Select HPMC E5:
It has a low viscosity, resulting in ease of application in aqueous or organic solvent systems.
It has exceptional film formation properties to ensure a defect-free and uniform surface covering.
It has exceptional clarity for product displays, so the coating can often be colored and not appear hazy.
It demonstrates predictable performance in lab-scale and large-scale productions.
By selecting HPMC E5, the formulator achieves better clarity compared with other grades of HPMC. Consistent quality of the coating translates into predictable stability performance and, therefore, reliable batch failure.
Added benefit beyond stability
While protecting the API in a tablet is critical for the effective product, HPMC coatings also offer a patient advantage:
Better swallowing: The smooth and shiny surface of the HPMC coater tablet makes it easier to swallow. This matters especially to patients who have trouble swallowing tablets.
Taste Masking: Bitter or unpleasant flavors can be masked, increasing patient adherence.
Aesthetics/Look: A coated product is usually more aesthetically pleasing and helps users recognize and trust the brand.
For patients, these aspects may appear insignificant– they matter when it comes to adherence to medication regimens.
Challenges and Factors
Every industry and technology comes with challenges. When it comes to HPMC coatings, for instance, the main challenges are:
Processing time: Aqueous HPMC coatings generally require more drying time than some synthetic polymer coatings.
Moisture sensitivity during production: Thus, moisture control is a consideration in the production environment.
Cost: While HPMC coatings are not necessarily exorbitant and are more expensive than some other types of coatings, they can be more expensive than budget-conscious projects would prefer.
However, these challenges are generally outweighed by the long-term stability, reduced risk of recall, and the improved experience for the patient.
The Future of HPMC Tablet Coatings
Development of formulation science seems to be continually re-shaping expectations for HPMC coatings. We are already seeing things such as:
Nanocoatings with even better moisture and oxygen barriers without increasing coating thickness.
Functional multi-layer systems with HPMC being the inner/first coat and specialized outer layers that may provide UV protection or triggering release.
Eco-label compliant solvent systems that reduce impacts and still behave similarly to organic solvent systems.
As research continues to grow, HPMC coatings, especially high-performance grades such as E5, will continue to be an integral part of the stability strategies used by pharmaceutical companies.
Conclusion: A Proven Shield for Contemporary Medicine.
The benefits of HPMC tablet coatings on stability and shelf life cannot be overstated. By providing an effective barrier against moisture, oxygen, light, and mechanical stress, HPMC coatings ensure that medicines are still safe, effective, and consistent through their duration of use.
While HPMC E5 is dependent on its unique sweet spot of performance and processability, and has been used continuously worldwide by formulators, it still requires processing, must be maintained at the optimum thickness, and stored effectively. However, for both manufacturers and patients, the overall returns for HPMC E5 tablet coatings are immense.
Sandip Agrawal, Polymer Engineer and MD of Sakshi Chem Sciences Pvt. Ltd., leads innovation in construction chemicals, shuttering oils, and industrial lubricants. With expertise in polymer science and eco-friendly solutions, he drives R&D and sustainable advancements, ensuring high-performance products for India and global markets.