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Oral Drug Delivery Systems: Delayed-Release Systems

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Oral delayed-release systems are modified-release formulations that postpone drug release until reaching a specific site in the gastrointestinal tract, usually the intestine.

These systems address challenges such as gastric irritation and acid-induced drug degradation. Also, they contribute to achieving localized therapeutic action within the intestine.

They typically employ enteric coatings made of pH-sensitive polymers like cellulose acetate phthalate or methacrylic acid copolymers.

These coatings prevent drug dissolution in the stomach’s low pH and enable release in the higher intestinal pH, minimizing gastric side effects.

Some examples include enteric-coated aspirin and diclofenac.

Delayed release systems are often classified as intestinal or colonic release systems, depending on the target site within the gastrointestinal tract.

Some formulations—such as mesalamine—also act as targeted-release systems, releasing the drug in the terminal ileum and colon.

Overview

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Delayed-release drug delivery systems are specialized pharmaceutical formulations designed to postpone the release of active compounds until the drug reaches a specific region of the gastrointestinal (GI) tract, typically the intestine. These systems are essential for drugs that may cause gastric irritation, are unstable in acidic environments, or need to exert therapeutic effects locally in the intestinal or colonic regions.

The core feature of delayed-release systems is the use of enteric coatings—polymer films that resist dissolution in the acidic gastric environment (pH ~1–3) and dissolve at the higher pH levels found in the intestine (pH ~5–7.5). Common polymers include cellulose acetate phthalate and methacrylic acid copolymers, which provide site-specific protection and control over drug release. By employing these pH-sensitive materials, the drug remains intact as it passes through the stomach and begins to dissolve only upon reaching the intestinal milieu, thereby reducing gastric side effects and enhancing therapeutic efficacy.

Delayed-release formulations are particularly valuable for nonsteroidal anti-inflammatory drugs (NSAIDs) like aspirin and diclofenac, which can cause gastric mucosal damage when released in the stomach. These formulations reduce gastrointestinal irritation by delaying release until the drug reaches the intestine. Further specialization within delayed-release systems includes targeted-release strategies. For instance, mesalamine is designed to be released in the terminal ileum and colon, treating inflammatory bowel diseases like ulcerative colitis and Crohn’s disease. These systems may use time-dependent mechanisms in combination with pH-sensitive coatings or incorporate biodegradable polymers activated by colonic bacteria to achieve precise drug localization.

Delayed-release technologies exemplify how pharmaceutical formulation strategies can align drug delivery with physiological conditions, optimizing therapeutic outcomes while minimizing systemic side effects.

Transcript

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Delayed Release Systems

Enteric Coatings

pH Sensitive Polymers

Gastrointestinal Tract

NSAID Formulations

Targeted Release

Colonic Delivery

Biodegradable Polymers

Therapeutic Efficacy