Preparation And Evaluation Of Esalazine Rectal In Situ Temperature-sensitive Gel

ObjectiveIn the targeted treatment of ulcerative colitis,mesalazine was used as a drug substance,and the formulation and preparation process of the formulation were optimized,and the mesalazine rectal in situ temperature-sensitive gel was prepared.The key functions such as thermosensitivity,gelation,targeting adhesion and location were also elucidated.MethodThe raw materials were pulverized by mechanical pulverization,jet pulverization,high pressure homogenization and ball milling,respectively.The particle size of the material was determined by Malvern particle size analyzer,and the in vitro release of the temperature-sensitive gel prepared by different pulverized materials was determined to determine the optimum pulverization process.The gelation temperature of the gel was determined by the test tube inversion method;the gelation temperature and process feasibility were used as evaluation indexes,and the preparation process was screened.The gelation temperature was used as an evaluation index to screen thermosensitive polymer materials and gelation temperature regulators.The rectal retention in the body was used as an evaluation index to screen the types and models of bioadhesives,and to examine their effects on in vitro release.The dosage of poloxamer 407,poloxamer 188 and hypromellose was optimized by star point design-effect surface method.The best prescription was further screened by examining the rectal retention and in vitro release in vivo.The rheometer was used to investigate the effect of different amounts of excipients on the change of elastic modulus（G’）with temperature and to determine the change of G’with temperature during gelation.A HPLC method was developed for the determination of mesalazine and its related substances in thermosensitive gel.A method for the determination of mesalazine in release medium was established,and the factors affecting the release rate were also investigated.Taking the relevant substances as indicators,the effects of strong light,high temperature and low temperature freeze-thaw on the preparation were investigated,and the stability of the preparation was preliminarily evaluated.Rats were given normal saline and temperature-sensitive gel for 7 consecutive days.The rectum was taken out and the histopathological changes were examined by light microscopy.The mucosal irritation of mesalazine rectal temperature-sensitive gel was compared and evaluated.SD rats were divided into three groups by mesalazine solution,mesalazine solution enema,mesalazine temperature-sensitive gel enema,and blood and rectal tissue were taken at a certain time.The concentration of drug in plasma and rectum was determined by HPLC-MS.The pharmacokinetic parameters were obtained by DAS software,and the rectal targeting efficiency and targeting index were calculated to evaluate the rectal positioning effect of the preparation.ResultThe best pulverization process was mesalazine.The air pulverization treatment was used as ultrafine powder,and then 0.7%SDS was used as a stabilizer.The nano-materials werehomogenized 30 times under the conditions of 15 000 psi pressure and 35 feeding speed by high-pressure homogenizer.The optimal preparation process was to take the above-mentioned nano-sized homogenizing liquid in sufficient amount,and successively added preservative（benzapium bromide）,bioadhesive（hypromellose）,temperature regulators（poloxamer 188）and temperature-sensitive materials（poloxamer 407）successively under continuous stirring,added water to the full amount,stirred to make the excipients evenly dispersed,and freezed in the refrigerator until completely swelled and dissolved.The optimum prescription was 6.7%mesalazine,1.1%HPMC,26%P188,17.35%P407,0.02%benzalkonium bromide and32.1℃gelation temperature through star design-response surface methodology（CCD-RSM）.Accordingtotheresultsoftherectalretentiontest,the temperature-sensitive gel could gel at body temperature and stay for more than 6 h.From G’results,P407,P188,HPMC and raw material homogenate could increase G,while G’slope did not change the gel mechanism.As the temperature increases,the G’value of the preferred prescription changed in the S curve,and the G’value in the liquid state was extremely low.When it rised to a certain temperature,G’rapidly increases,indicating that the gel underwent a phase transition when fully transformed.When it was semi-solid,G’did not change substantially.The gelation temperature measured by the rheometer and the tube inversion method was substantially the same.The in vitro release results showed that the gel could achieve sustained release for8 h,and the release behavior in pure water was significantly different from that of pH6.5 and pH 7.4 PBS buffer,and the release in pH 7.4 PBS buffer was faster.;The release curves at different speeds were compared in pairs,and the f₂ values were all greater than50,indicating that there was no significant difference in the release of the different rotational speeds.The stability test results showed that high temperature,strong light,low temperature freeze-thaw would increase the related substances,indicating that the gel preparation should avoid high temperature,strong light and low temperature freezing and thawing.According to the pharmacokinetic results,the AUC of the temperature-sensitive gel rectal tissue was 3.47 times that of the solution enema and 2.51 times of the solution gavage,indicating that the temperature-sensitive gel can increase the local drug concentration of the rectum compared with the solution enema and solution gavage,and the rectal positioning is given.The drug has significant advantages.After the rats were given temperature-sensitive gel for 7 consecutive days,there was no obvious hyperemia and pathological changes in the rectum.The mesalazine rectal temperature-sensitive gel showed no obvious irritation to the rat rectal mucosa.ConclusionThe optimal formulation composition and preparation process of mesalazine rectal in situ temperature sensitive gel were clarified.The preparation achieved the desired temperature-sensitive gel performance,had suitable gel strength,could be retained in the rectum for a long time,had a significant advantage in rectal positioning,and had no obvious mucosal irritation,showing a good application prospect.