Rl30d

Metformin (M, 98%), sodium alginate (SA, 99%), chenodeoxycholic acid (CDCA, 99%) and Poloxamer 407 were purchased from Sigma Chemical Co (St. Louis, MO, USA). Eudragit^® RS30D, RL30D and NM30D polymers were supplied by Evonik Industries (Essen, Germany). Calcium chloride dihydrate (CaCl₂ 2H₂O 98%) was obtained from Scharlab S.L (Barcelona, Spain). All reagents and solvents were HPLC grade, used without further purification or modification and were supplied by Merck (Bayswater, VIC, Australia).

Tetrodotoxin (purity≥98%) was provided by ZhaoYang Biopharma Co., Ltd. (Xiamen, China). Sugar sphere (600–710 μm) and microcrystalline cellulose sphere (500–710 μm) were purchased from JRS Pharma Co., Ltd. (Rosenberg, Germany). Opadry (YS-1-7006) was purchased from Colorcon Co., Ltd. (Shanghai, China). Hydroxypropyl methylcellulose (E5) was purchased from Huzhou Zhanwang Pharmaceutical Co., Ltd. (Huzhou, China). 1-octanesulfonate sodium was provided by REGIS Technologies (Morton Grove, IL, USA). Sodium phosphate monobasic dehydrate, sodium phosphate dibasic dehydrate, sodium hydroxide, phosphoric acid and acetonitrile were provided by Sinopharm Chemical Reagen Co., Ltd. (Shanghai, China). Triethyl citrate was provided by Shanghai Macklin Biochemical Co., Ltd. (Shanghai, China). Talc (10 μm) was purchased by Guangxi Longsheng Huamei Talc Development Co., Ltd. (Guilin, China). Citric acid was purchased from Taishan Xinning Pharmaceutical Co., Ltd. (Taishan, China). Poly (1-carboxyethylene) (Eudragit NE 30D, RS 30D, RL 30D, L30D-55) was purchased from Evonik Industries AG (Darmstadt, Germany).

Neutral pellets 700–810 µm (Sugar spheres, Hanns G. Werner GmbH, Tornesch, Germany) were coated in two separate coating steps. For a layering process, water suspension composed of 15.9% w/w model drug in a form of weak acid salt, 1.9% w/w talc (Imerys Talc S.p.A., Porte, Italy) and 1.2% w/w hydroxypropyl cellulose (Ashland Specialty Ingredient g.p., NJ, USA) was used. For prolonged release, a coating combination of low and high permeable copolymer types of ethyl acrylate, methyl methacrylate and different levels of methacrylic acid ester with quaternary ammonium groups, i.e., Eudragits RS 30D (9.6% w/w) and RL 30 D (19.2% w/w) (Evonik Industries AG, Darmstad, Germany), with 1.7% w/w triethyl citrate (Vertellus LLC, Indianapolis, IN, USA) and 10.4% w/w of talc (Imerys Talc S.p.A., Porte, Italy) was used. All other materials used for dissolution tests were of analytical grade and were supplied commercially.