1. pH level of the digestive tract
The core principle of enteric-coated capsule design is to pass through the stomach without releasing the drug there, but to dissolve and release the contents in the intestines at a higher pH. This mechanism relies on the difference in pH values ​​at different parts of the digestive tract. The pH value of the stomach is usually low, between 1.5 and 3.5, and this highly acidic environment will corrode the shell of ordinary capsules, but for enteric-coated capsules, their shells are specially designed to resist the erosion of gastric acid and will not dissolve until the capsule enters the intestine (pH 5.5 to 7.5). The individual differences in pH values ​​in the digestive tract are large, especially in different health states. For example, patients with indigestion or abnormal gastric acid secretion may have a pH value in the stomach or intestine that deviates from the normal range, which will affect the dissolution of enteric-coated capsules and the release time of drugs. Therefore, understanding and monitoring the pH level of the patient's digestive tract is crucial to ensure the effectiveness of the drug. In addition, different diseases or drugs may also affect the pH value of the digestive tract, thereby affecting the absorption effect of enteric-coated capsules.

2. Coating material and thickness
The coating material and thickness of enteric-coated capsules directly affect their dissolution rate and drug release time. Common enteric materials include cellulose acetate phthalate (CAP) and polyvinyl alcohol phthalate (PVAP). These materials are well tolerated in gastric acid but gradually dissolve in alkaline environments. The thickness of the coating is an important variable. Thicker coatings usually take longer to dissolve, which means that the release time of the drug will be delayed, which may affect the efficacy of the drug. If the coating is too thin, it may begin to dissolve in a slightly acidic environment, which will cause the drug to be released prematurely in the stomach, which may cause stomach discomfort or reduce the efficacy of the drug. In addition, different coating materials have different dissolution properties. Some materials may remain stable at lower pH values, while others will dissolve faster. Drug manufacturers usually choose coating materials and thickness based on the characteristics of the drug, the needs of the patient, and the desired release location.

3. Digestive tract transit time
The design goal of enteric-coated capsules is to ensure that the drug is not released in the stomach, but dissolves after reaching the intestine smoothly. Therefore, the transit time of the capsule in the digestive tract (i.e., the speed of movement from the stomach to the small intestine) is crucial to the effect of the drug. Under normal circumstances, the time that food or drugs stay in the stomach affects the speed at which the capsule enters the intestine. If the gastric emptying time is too long, the enteric-coated capsule may begin to dissolve before reaching the intestine, and the drug may be released at the wrong location, which will affect its absorption and efficacy. On the contrary, if the transit time is too fast, the capsule may be expelled before reaching the ideal location in the intestine, resulting in inadequate release of the drug. Factors that affect the digestive tract transit time include diet, digestive health, gastrointestinal dysfunction, etc. For example, patients with delayed gastric emptying or irritable bowel syndrome may experience different capsule transit times, which may affect drug absorption.

4. Drug formulation and solubility
The drug formulation and dissolution properties in the enteric-coated capsule have a significant impact on the absorption rate of the drug. Different drugs have different physicochemical properties, such as particle size, solubility, and chemical stability, which will affect their dissolution and absorption rate in the intestine. Generally, the smaller the drug particles, the faster the dissolution rate and the higher the absorption rate. However, some drugs have low solubility and may require special formulation technology to ensure their effective absorption. If the drug does not dissolve adequately or dissolves too slowly in the intestine, absorption will be limited, which may lead to reduced efficacy. In addition, drug stability is also a key factor. Some drugs may be sensitive to the environment and begin to decompose or lose activity before entering the target absorption site. In order to optimize the release and absorption of the drug, drug developers usually need to conduct multiple tests on the drug formulation to find the right particle size, formulation additives and coating design to ensure that it can be stable and fully dissolved in the intestine.

5. The influence of food and other drugs
Food and other drugs have an important influence on the dissolution and absorption of enteric-coated capsules. First, food delays gastric emptying, causing the capsule to stay in the stomach longer, which may lead to a delay in dissolution time. Especially high-fat foods, which will further prolong digestion time and affect the release rate of drugs in the intestine. In addition, certain types of food will change the pH of the stomach and intestine, thereby affecting the dissolution of the enteric coating. For example, acidic or alkaline foods may change the pH environment of the digestive tract, causing the enteric coating to dissolve earlier or later. At the same time, other drugs, especially antacids or drugs that inhibit gastric acid secretion, such as proton pump inhibitors (PPIs) or H2 receptor antagonists, can also significantly affect the effectiveness of enteric-coated capsules. They reduce gastric acid secretion and change the pH value of the stomach and intestines, which may cause the enteric coating to dissolve prematurely in the stomach and release the drug in the wrong place. Therefore, when prescribing enteric-coated capsules, doctors usually advise patients to pay attention to meal times and use them in conjunction with other drugs to ensure that the drug can be released in the intestine as expected and effectively absorbed.