Mesalazine is an anti-ulcer drug that exerts its efficacy locally in the lesion, rather than as a systemic efficacy drug. It exerts a significant anti-inflammatory effect on the intestinal wall mainly by acting directly on local inflammatory sites in the intestinal mucosa, inhibiting the synthesis of prostaglandins that cause inflammation and the formation of leukotrienes, the mediators of inflammation. In addition, mesalazine can inhibit lipoxygenase activity of neutrophils and certain functions of neutrophils (such as migration, degranulation, phagocytosis and oxygen radical synthesis). Depending on the drug excipients, acetylsalicylic acid is released in different intestinal segments after oral administration, and part of it is decomposed by bacteria in the intestinal tract and excreted in the feces, while the other part is absorbed by the intestinal mucosa, and about 40% is bound to plasma proteins and metabolized in the body to produce acetylates, and about 80% of these acetylates are bound to plasma proteins and excreted in the urine. The half-life is 5-10 hours. The above mechanism of action of mesalazine shows that a drug is good or bad, and whether it can make the oral drug directly on the lesion part has a relationship, premature metabolism of the drug, can not play a therapeutic role. Gastrointestinal pH during physiological and Crohn’s disease states The pH of the gastrointestinal tract varies in different segments of the intestine in normal subjects, from about 6.0-6.5 in the ileocecal region to about 6.5-8.0 in the colon. pH of the ascending colon is often reduced to about 6.4±0.6 due to bacterial fermentation producing short-chain fatty acids. pH of the ascending colon often decreases during inflammation, e.g., ascending colon pH can drop to 4.7±0.7 in patients with Crohn’s disease. and The pH state of the intestine and its alterations play a crucial role in influencing the release and efficacy of mesalazine drugs. Classification and action characteristics of oral formulations of mesalazine Oral formulations of mesalazine are mainly divided into tablets and granules according to their appearance. Tablets are released by disintegration and dissolution, characterized by slow absorption and distribution, relatively obvious sudden drug release effect and high local therapeutic concentration. The granules are directly dissolved, which are absorbed and distributed faster, and the sudden release effect is more moderate and the local concentration is slightly lower. According to the main drug excipients used, mesalazine can be divided into extended-release tablets and controlled-release tablets. The so-called extended-release tablets are tablets with suitable excipients that release the drug and the excipients more slowly and have a longer-lasting effect. Compared with ordinary tablets, extended release tablets have the advantages of long-lasting effect and less times of taking; while controlled release tablets are made of suitable skeleton material, and the drug and skeleton material are made to be released under specific conditions, the release of ordinary tablets is uncontrollable and disintegrates quickly, while controlled release tablets realize the controlled release of drug and can well achieve the effect of local treatment. Regardless of whether it is a slow release tablet or a controlled release tablet, the main breakthrough point lies in the drug excipients, and there are two main types of drug excipients, namely acrylic resin and ethyl cellulose. Acrylic resin is a pH-dependent drug excipient that dissolves only under specific pH conditions, while ethyl cellulose is pH-independent. According to the pH dependence, acrylic resins are further classified into Eudragit L and Eudragit S. Eudragit L starts to dissolve at pH ≥ 6, while Eudragit S dissolves only at pH ≥ 7, which is the mechanism by which the drug release of mesalazine controlled release tablets is precisely controlled. Integrating the above several classification indicators, specifically I denote the three commonly used manufacturers producing oral formulations of mesalazine as A, B and C respectively (circumventing the specific manufacturer), these three different dosage forms have their own characteristics and the patients they target are different: A drug mainly uses Eudragit L as the drug excipient, which is a pH-controlled, time-dependent drug with the active ingredient at Therefore, for Crohn’s disease patients whose lesions are mainly in the terminal ileum and colon, the use of drug A can maintain a high local therapeutic concentration in the inflamed intestinal segment and achieve a better therapeutic effect, while reducing drug waste. Therefore, for Crohn’s disease patients whose lesions are mainly in the colon, drug B can maintain a higher local therapeutic concentration in the inflamed intestinal segment and achieve a better therapeutic effect, while reducing drug waste. C drug, with ethyl cellulose as the drug excipient, is only a time-dependent drug, and the active ingredient starts to be released in the stomach, and the distribution range is the whole intestine. Although the selection of C drug can make the active ingredient of the drug released in the whole intestine, the same single dose, the therapeutic concentration is relatively low, the targeting is not strong, the drug is wasted seriously, and the drug often has difficulty in reaching the distal colon. At the same time, for patients with gastric and duodenal ulcers, drug C is a prohibited drug. Mesalazine suppositories: For patients with lesions in the rectum or the terminal colon, suppositories for topical use are also available. Suppositories are broadly divided into A and B according to their characteristics: A suppositories mainly have the following advantages: ① the shape is designed with human anatomy and physiology in mind, it is easier to enter the rectum under the contraction of the anal sphincter, not easy to slip off, convenient to administer, and relatively comfortable for patients to use; ② the suppositories can be quickly dissolved after entering the rectum to release the active ingredients, with faster onset of action; ③ the suppositories use a fat-soluble matrix as the skeleton material. The surface is smooth and has good affinity with intestinal mucosa, so that the drug can easily bind to the ulcerated mucosa with high local concentration and significant therapeutic effect. In comparison, B suppository has the following disadvantages: ① the surface is dry, difficult to squeeze into the dry anus, additional water-soluble lubricant is needed to assist the anal plug; ② poor solubility in water, difficult to dissolve in the dry rectum, can not quickly release the active ingredients; ③ foreign body feeling is strong, the patient’s comfort is not good; ④ hard texture, the surface has angles, for patients with rectal mucosal injury may cause secondary damage. V. Mesalazine enema solution: For patients with lesions in the rectum or terminal colon, you can also choose a local enema solution. Enema solution according to its characteristics are also divided into two kinds: A enema solution mainly has the following advantages: ① soft drug delivery tube, the outside of the tube wrapped with a smooth film, inserted into the anus more smooth, better comfort; ② one-way liquid valve, to avoid reverse absorption of intestinal fluid; ③ storage bottle using the “accordion” type structure, squeeze the liquid more effort In contrast, the B enema solution has the following characteristics In contrast, B enema solution has the following disadvantages: ① hard drug delivery tube, inserted into the anus foreign body feeling is very strong, and easy to cause damage to the rectal mucosa; ② no one-way valve, in the process of patient enema easy to cause intestinal fluid back in the reservoir bottle, resulting in pollution; ③ hard reservoir bottle, squeeze the liquid relatively laborious, and often difficult to completely extrude, resulting in drug waste.