Study On Thermosensitive Gel Enema Of 5-aminosalicylic Acid

Ulcerative colitis?UC?is a chronic non-specific inflammatory bowel disease that its etiology and pathogenesis have not been known clearly.5-aminosalicylic acid?5-ASA?remains the first-line treatment for mild to moderate active and remissive ulcerative colitis because of definite efficiency,sufficient evidences and less side effects.5-ASA is available in oral and rectal preparations.Compared with oral administration,rectal administration which includes suppository and enema,offers the advantage of delivering a known amount of 5-ASA topically to the distal colon.However,both of them have flaws in clinical use.Suppository can only act on rectum and the contact area with lesions is limited.Although enema can reach sigmoid colon,a lack of bioadhension leads them to remain for a short time inside the colon by the influence of peristalsis.Aiming at the existing drawbacks of rectal administration,a 5-ASA thermosensitive gel enema that is suitable for the topical treatment of colitis was developed in this paper.Poloxamer,polycarbophil and sodium hyaluronate that are good biocompatible polymers were used as thermosensitive materials and bioadhensive materials.This paper mainly reported formula optimization,rheological properties,in vitro release profiles,quality control,preliminary stability,in vivo pharmacodynamics and topical irritation of 5-ASA thermosensitive gel enema.5-ASA thermosensitive gel enema was prepared by cold dissolving method.Based on the result of single factor experiments,central composite design-response surface methodology was used to optimize the formula with the amount of P407,P188 and PCP as the influencing factors,the gelation temperature,viscosity before gelling and sedimentation ratio as the indices.The optimum ratio of P407,P188 and PCP was 17.6%,8.0%and 0.15%,the observed gel temperature was about 33.7?,viscosity before gelling was385mPa·s,and the sedimentation ratio was 99.2%.The rheological properties were determined by rotational rheometer.The results showed that the formula had excellent temperature sensitivity,it presented free-flowing liquid with low viscosity at room temperature and became gel with high viscosity and pseudoplastic characteristics at the body temperature,which makes it suitable for rectal administration.The dynamic membrane dialysis method and UV-vis spectrophotometry were used to determined in vitro release profiles of 5-ASA thermosensitive gel enema.The results showed that 42.8%of drug was released in the first 2h,74.2%of drug was released from the gel after 4h,and the drug could be released completely during 8h.Compared with mesalazine enema,the drug release was significantly delayed in the thermosensitive gel system.Drug release curve was fit with Higuchi equation:Q=0.4289t^1/2-0.1593,r=0.9915,which indicated that the 5-ASA release from thermosensitive gel followed a matrix diffusion controlled mechanism.The content and related substances of 5-ASA thermosensitive gel enema were determined by HPLC.The quality could be controlled by evaluating the indexs such as the appearance,gelation temperature,pH,viscosity,sedimentation ratio,the content and related substances.Preliminary stability was evaluated as well.The results showed that the quality of 3 batches of5-ASA thermosensitive gel enema met the related requirements.The test of influencing factors suggested that 5-ASA thermosensitive gel enema was sensitive to high temperature and illumination and should be preserved at light-resistant and cool place.6-month accelerated test and long-term test indicated that the quality of the preparation was stable however longer stability test was under investigation.Ulcerative colitis model was induced by dextran sulfate sodium in BALB/c mice to investigate the in vivo pharmacodynamics.The clinical parameters such as body weight changes,stool consistency and occult bleeding were evaluated.In addition,macroscopic score and histological score of colon was conducted to assess the severity of mucosal damage and inflammation infiltrate.The results showed that rectally administered 5-ASA formulations had significant therapeutic effects on ulcerative colitis in mice model,and 5-ASA thermosensitive gel had better effects than mesalazine enema owing to reducing leakage of drugs.Finally,the colonic mucosa irritation experiment was performed in SD rats.The results showed that 5-ASA and the excipients did not cause irritation and damage to colonic mucosa.In summary,the formula and preparation technics of 5-ASA thermosensitive gel enema described in this paper is simple and applicable.It has great temperature sensitivity,sustained-release effect and good stability.5-ASA thermosensitive gel enema has good biocompatibility and can help to reduce leakage of drugs and extend residence time inside the colon.Therefore,5-ASA thermosensitive gel enema may improve therapeutic effect comparing with traditional formulations on distal colitis and provide a better choice for the treatment for distal colitis.