An enteric coating is a specialized polymeric barrier applied to oral medications, such as tablets or capsules. The term “enteric” refers to the small intestine, defining the coating’s primary goal: to keep the medication intact as it passes through the highly acidic environment of the stomach. This layer is engineered to ensure the drug only dissolves and releases its active ingredient after it has safely moved beyond the stomach and into the upper digestive tract.
Why Medications Need Enteric Coatings
The digestive system presents two major challenges that enteric coatings are designed to overcome, primarily related to the stomach’s harsh conditions. Stomach acid, which has a very low pH (typically 1.5 to 3.5), can chemically degrade certain drug compounds. Medications sensitive to acid, such as some antibiotics or protein-based drugs, would be rendered ineffective if released prematurely in the stomach.
The coating ensures that the full dose of the drug remains viable until it reaches the small intestine, where it can be properly absorbed. Without this protective layer, the body would receive a significantly reduced therapeutic dose, compromising treatment efficacy. This mechanism ensures the drug reaches its intended absorption site in its active chemical form.
The second function of the enteric coating is to protect the lining of the gastrointestinal tract from the medication itself. Certain pharmaceutical agents, including common pain relievers like aspirin and nonsteroidal anti-inflammatory drugs (NSAIDs), can be irritating to the stomach mucosa. If released directly into the stomach, these drugs can cause localized damage, leading to irritation, nausea, or the formation of ulcers.
By delaying the release until the medication reaches the small intestine, the coating prevents prolonged contact between the irritant drug and the stomach wall. The small intestine is less sensitive to these compounds, allowing the drug to be rapidly diluted and absorbed once released. This enhances patient tolerance and reduces the risk of gastrointestinal side effects.
How the Coating Works
The functionality of an enteric coating is based on a precise chemical mechanism that relies on the pH differences found throughout the digestive tract. The coating material is typically a polymer containing acidic functional groups, which act as chemical “switches” controlling solubility. In the stomach’s highly acidic environment (pH 1.5–3.5), these acidic groups remain in an uncharged, non-ionized state.
In this non-ionized form, the polymer is insoluble, meaning the coating remains solid and resistant to dissolution by the gastric fluid. The medication is locked inside its protective shell for the duration of its stay in the stomach. This resistance ensures the drug is not released until it has passed through the pyloric valve.
Once the dosage form empties into the small intestine, the environment becomes less acidic, with a pH that rapidly rises to 5.5 to 7.5. This higher, more alkaline pH causes the acidic functional groups on the polymer chains to ionize, giving them a negative charge. The ionized polymer becomes water-soluble, causing the coating to swell, dissolve, and disintegrate. This pH-triggered dissolution allows the active drug ingredient to be released exactly where it is intended to be absorbed.
Safe Handling and Compromising the Coating
The integrity of the enteric coating is directly tied to the drug’s effectiveness and patient safety, making proper handling non-negotiable. Crushing, chewing, or cutting an enteric-coated tablet or capsule destroys the polymer layer. When this physical barrier is compromised, the drug’s intended delayed-release mechanism is instantly bypassed.
The consequences of damaging the coating are twofold, leading to a failure of both protective functions. First, if the medication is sensitive to acid, the exposed drug is immediately subjected to the stomach’s low pH. This leads to chemical degradation, reducing therapeutic potency and resulting in an inadequate dose reaching the bloodstream.
Second, if the medication is an irritant, its premature release directly into the stomach lining can cause severe gastric distress or chemical injury. Patients who have difficulty swallowing a whole tablet must never manipulate the drug themselves. They should consult a pharmacist or physician for an alternative, non-enteric formulation, such as a liquid or a non-coated version, that is safe for immediate release.