Credo Life Science
Posted on 27th January 2022
How Enteric Coated Pellets Protect Drugs from Stomach Acid
The human stomach is a hostile environment for many pharmaceutical drugs. With a pH ranging from 1 to 3 — comparable to concentrated lemon juice or vinegar — gastric acid is powerful enough to degrade, inactivate, or chemically alter a wide range of active pharmaceutical ingredients before they even reach the site where absorption can occur. For such drugs, swallowing a conventional tablet or capsule means that much of the dose is destroyed in the stomach and never reaches the bloodstream.
Enteric-coated (EC) pellets solve this problem with elegant precision. A thin layer of pH-responsive polymer — invisible to the naked eye but scientifically sophisticated — wraps around each individual pellet and acts as a protective shield in the acid environment of the stomach, then dissolves instantly upon reaching the alkaline pH of the small intestine, releasing the drug exactly where absorption can occur.
Credo Life Sciences manufactures WHO-GMP certified enteric-coated pellets for pharmaceutical companies in India and internationally, supporting products from early development through commercial supply. This blog explains the complete science of how enteric coating works, which drugs need it, and how EC pellets deliver protection and precision simultaneously.
Understanding the Stomach's Chemical Environment
The stomach secretes hydrochloric acid (HCl) as part of its digestive function, creating an acidic environment (pH 1.2–3.0 in the fasting state, rising to pH 4–5 after food ingestion) that serves to sterilise ingested food, begin protein digestion, and activate digestive enzymes. For the digestive system, this acidity is essential. For certain pharmaceutical molecules, it is destructive.
- Acid-labile drugs: molecules that are chemically degraded, hydrolysed, or deactivated by gastric acid — they simply don't survive the stomach intact in sufficient quantity to be clinically effective without protection
- Gastric irritants: drugs that are chemically stable in acid but cause mucosal irritation, ulceration, or bleeding when concentrated in the gastric environment — protection benefits the patient's stomach, not the drug molecule
Drugs that are vulnerable to the gastric environment fall into two main categories:
Drugs That Require Enteric Coating
Acid-Labile Proton Pump Inhibitors (PPIs)
Ethyl cellulose is a water-insoluble polymer that forms an impermeable film. Drug release is achieved by incorporating a water-soluble pore former — typically HPMC or PEG — into the EC film. Upon contact with gastrointestinal fluid, the pore former dissolves, creating microscopic channels through which drug diffuses. The release rate is controlled by the ratio of EC to pore former and the total coating weight gain.
Proton pump inhibitors — omeprazole, pantoprazole, esomeprazole, rabeprazole, lansoprazole — are the world's most prescribed drugs for acid-related disorders including GERD, peptic ulcer, and H. pylori eradication. The irony is profound: drugs designed to suppress acid secretion are themselves rapidly degraded by stomach acid. Omeprazole, for example, has a half-life of less than 2 minutes at pH 1.
Without enteric coating, PPIs are essentially inactive. With enteric-coated pellets, the drug survives gastric transit intact and is released in the duodenum where it can be absorbed and transported to the proton pumps of the gastric parietal cells to exert its acid-suppressing effect.
Pancreatic Enzyme Preparations
Pancreatic enzymes (pancrelipase — lipase, amylase, protease) used in exocrine pancreatic insufficiency (cystic fibrosis, chronic pancreatitis, post-pancreatectomy) are biological molecules that are immediately denatured by stomach acid. Enteric-coated enzyme micropellets allow enzymes to survive gastric transit and be released in the duodenum — where they are needed to assist digestion at the site of action.
Gastric Irritants: NSAIDs, Aspirin, Iron
Non-steroidal anti-inflammatory drugs (NSAIDs) such as diclofenac, naproxen, and indomethacin, low-dose aspirin, and iron supplements cause gastric mucosal irritation and ulceration through both topical (direct mucosal contact) and systemic (prostaglandin inhibition) mechanisms. Enteric coating provides a practical solution by preventing these drugs from contacting the gastric mucosa — they pass through the stomach without dissolving and are released only in the intestine where mucosal irritation is less problematic.
Budesonide for Intestinal Conditions
Budesonide formulated as enteric-coated pellets with release targeted to the ileum and colon is used in Crohn's disease and microscopic colitis. The enteric coating precisely targets drug release to the site of intestinal inflammation — maximising local therapeutic action while minimising systemic absorption and the associated steroid side effects.
The Chemistry of Enteric Coating: pH-Responsive Polymers
Eudragit L30D-55 and L100-55 (Methacrylic Acid Copolymer, Type A)
The most widely used enteric polymer for PPI pellets and other applications requiring intestinal release. Dissolves at pH > 5.5 — onset of dissolution occurs in the duodenum (pH typically 5.5–6.0). Applied as an aqueous latex dispersion, making it environmentally friendly and compatible with heat-sensitive APIs.
The key to enteric coating is the use of polymers that are pH-responsive — insoluble at low pH (gastric environment) but soluble at higher pH (intestinal environment). These polymers contain acidic functional groups — typically carboxylic acid groups — that are protonated (uncharged) at low pH, making the polymer hydrophobic and insoluble. At higher pH, these groups are deprotonated (charged), making the polymer hydrophilic and soluble. The transition from insoluble to soluble occurs sharply at a characteristic pH threshold specific to each polymer.
- Coating threshold: pH 5.5
- Key applications: omeprazole, esomeprazole, pantoprazole pellets
- Typical coating level: 20–30% w/w over drug-loaded pellet core
Eudragit L100 and S100
Dry polymer grades that dissolve at pH > 6.0 (L100) and pH > 7.0 (S100) respectively. Used for applications where drug release should be targeted to the mid-jejunum or terminal ileum/colon. Often used in combination (L100:S100 blends) to achieve specific intestinal targeting.
- Eudragit L100: pH 6.0 dissolution — jejunal release
- Eudragit S100: pH 7.0 dissolution — ileal/colonic release
- Key applications: budesonide ileal release pellets, mesalazine colonic release pellets
HPMCP (Hydroxypropyl Methylcellulose Phthalate)
A cellulosic enteric polymer available in HP50 (dissolution pH 5.0) and HP55 (dissolution pH 5.5) grades. Provides excellent film-forming properties and compatibility with a wide range of APIs. Commonly used in Japanese and Asian markets.
HPMCAS (Hydroxypropyl Methylcellulose Acetate Succinate)
A cellulosic polymer with solubility transition pH adjustable by grade selection (LF/MF/HF grades dissolve at pH 5.5, 6.0, and 6.8 respectively). Widely used in amorphous solid dispersion applications where enteric release is required.
The Two-Stage Dissolution Test: How EC Pellets Are Verified
Stage 1 — Acid Resistance Test
Pellets are placed in 0.1 N HCl (pH 1.2) — simulating fasting gastric fluid — for 2 hours under standard paddle/basket conditions. Samples are taken and tested by HPLC. Specification: not more than 10% drug release. This test confirms that the enteric coat remains intact in the stomach environment — protecting acid-labile drugs from degradation and preventing premature release of gastric irritants.
Regulatory agencies globally — USFDA, EMA, WHO — require that enteric-coated products demonstrate both acid resistance and drug release in buffer through a two-stage dissolution test:
Stage 2 — Buffer Release Test
The medium is adjusted to pH 6.8 (or the appropriate intestinal pH for the specific product and target site). Dissolution continues for a further 45–90 minutes. Specification: not less than 75–80% drug release within the specified time. This confirms that once the enteric coat encounters the higher pH of the intestine, it dissolves rapidly and completely — releasing the drug for absorption. Credo Life Sciences conducts two-stage dissolution testing on every batch of EC pellets manufactured, using validated HPLC analytical methods developed and qualified in-house.
Manufacturing EC Pellets: The Wurster Coating Process
Reduced Adverse Effects
Key Process Controls
Enteric coating of pellets is almost universally performed in a fluid bed coater with a Wurster insert — a bottom-spray configuration that keeps pellets continuously circulating through a coating zone, depositing thin, uniform layers of enteric polymer with each pass. The Wurster process is the industry standard for EC pellet coating because it achieves the coating uniformity that is essential for consistent acid resistance.
- Coating weight gain: typically 20–35% for Eudragit L30D-55 systems — must be uniform across all pellets in a batch
- Inlet air temperature: governs film quality — typically 35–42°C for aqueous Eudragit dispersions
- Product temperature: maintained at 28–35°C to ensure film formation without over-drying
- Spray rate: matched to evaporation rate to prevent pellet agglomeration
- Plasticiser level: triethyl citrate (TEC) or diethyl phthalate (DEP) added to the coating dispersion to ensure film flexibility and prevent cracking
- Curing step: post-coating thermal treatment at 40°C for 24–48 hours to fully coalesce the polymer film
Credo Life Sciences EC Pellet Portfolio
Credo Life Sciences manufactures enteric-coated pellets for a broad range of therapeutic applications:
- PPI EC pellets: omeprazole, pantoprazole, esomeprazole, rabeprazole, lansoprazole — for MUPS tablets and pellet-in-capsule products
- NSAID EC pellets: diclofenac sodium, naproxen — for reduced GI irritation formulations
- Pancreatic enzyme EC micropellets: for cystic fibrosis and exocrine pancreatic insufficiency
- Custom EC pellets: development services for novel and generic molecules requiring enteric protection
Enteric-coated pellets represent one of the most scientifically elegant solutions in pharmaceutical formulation: a thin, pH-responsive polymer shield, individually applied to each tiny pellet, that perfectly protects acid-sensitive drugs and acid-producing drugs through the hostile gastric environment and then dissolves instantly upon reaching the intestine — delivering the drug precisely where it can be absorbed and exert its therapeutic effect.
Understanding the science of enteric coating — from polymer chemistry to Wurster process physics to two-stage dissolution validation — is essential for pharmaceutical scientists, formulators, and procurement professionals working with EC pellet-based medicines. Credo Life Sciences brings this expertise to every EC pellet project, from initial feasibility through validated commercial manufacturing.