A tablet coating is a thin, outer layer of material applied to the compressed core of a medication. While it can make the pill look appealing, the coating is a highly engineered and functional part of the drug delivery system. Its primary purpose is to ensure the medication works as intended from manufacturing until absorption. The specific chemical composition dictates its function, such as protecting the pill from the environment or controlling the timing and location of drug release within the body.
Essential Purposes of Tablet Coatings
One function of the applied film is to improve the patient experience by masking unpleasant qualities of the drug core. Many active pharmaceutical ingredients have a bitter taste or strong odor that can lead to difficulty swallowing. The film coating acts as a physical barrier, isolating the taste receptors from the disagreeable compounds until the pill is swallowed.
The coating also provides benefits for the drug’s shelf life and stability. The thin polymer layer shields the medication from environmental factors such as moisture, light, and air, which can chemically degrade the active ingredients. Protection from humidity is achieved by applying a film with low permeability to water vapor, slowing the degradation of moisture-sensitive compounds. Furthermore, the smooth surface of the film makes the tablet easier to swallow by providing lubricity as it travels down the throat.
How Coatings Control Drug Release
Beyond basic protection and taste masking, coatings are designed to dictate where and when the drug is released inside the digestive tract. One example is the enteric coating, which utilizes pH-sensitive polymers like methacrylic acid copolymers. The coating is insoluble and remains intact in the highly acidic environment of the stomach (pH typically between 1.5 and 3.0).
When the tablet passes into the small intestine (pH 6.0 to 7.4), the less acidic environment causes the polymer to dissolve quickly. This mechanism protects drugs, such as certain enzymes or proteins, that would otherwise be destroyed by stomach acid. It also prevents gastric irritation caused by medications like aspirin. This targeted release ensures the drug is delivered to the intended site for optimal absorption.
Extended-release or sustained-release coatings are engineered to slow the medication’s release over many hours. These coatings often use water-insoluble polymers, such as ethyl cellulose, which create a matrix or semi-permeable barrier around the drug particles. The drug is released gradually as intestinal fluid slowly penetrates the polymer film and dissolves the active ingredient. By controlling the coating’s thickness and composition, manufacturers regulate the rate of drug release, providing a steady therapeutic effect and often allowing less frequent dosing.
Why Coated Tablets Should Not Be Broken
Breaking or crushing a coated tablet compromises the engineered function of the outer layer. When a taste-masking film is broken, the full, unpleasant flavor and odor of the drug are immediately released, making the medication difficult to swallow. Compromising the coating can also have serious pharmacological consequences related to drug absorption.
For an enteric-coated tablet, breaking the film exposes the medication directly to stomach acid, which can destroy the drug before it reaches the small intestine, rendering it ineffective. For extended-release coatings, crushing the pill destroys the barrier controlling the gradual dissolution of the drug. This can lead to “dose dumping,” where the entire quantity of medication is released immediately into the bloodstream. This rapid release potentially causes a dangerous overdose or sudden, severe side effects due to a toxic peak concentration.