title: A controlled porosity osmotic pump system with biphasic release of theophylline.
abstract: A controlled porosity osmotic pump system with biphasic release of theophylline was developed for the nocturnal therapy of asthma. The developed system was composed of a tablet-in-tablet (TNT) core and a controlled porosity coating membrane. Release pattern of the developed system was influenced by amount of pore former (18.2-45.5%, w/w of polymer), weight gain (16-26 mg per tablet) of the coating membrane and osmotic agents used in inner layer of the TNT core. When sodium phosphate and sodium chloride were selected as the osmotic agents in inner and outer layer of the TNT core respectively, target release profile was obtained with coating solution cellulose acetate-polyethylene glycol 400-diethyl phthalate (54.5-36.4-9.1%, w/w) at a weight gain of 16-22 mg per tablet. To examine the mechanism of drug release, release profiles of osmotic agents, micro-environmental osmotic pressure and micro-environmental pH of the formulation during dissolution were studied. Micro-environmental osmotic pressure decreased and micro-environmental pH increased continuously during the whole dissolution process, theophylline release was dominated by the successive dissolution of sodium chloride and sodium phosphate. Theophylline solubility increased as environmental pH exceeded 10.8. At the last stage of the biphasic release, micro-environmental pH in the developed formulation reached 10.9, and theophylline release was promoted by its elevated solubility despite of the decrease of micro-environmental osmotic pressure in the developed formulaiton.
authors.affiliation: West China Pharmacy School, Sichuan University, Chengdu, China.
authors.forename: Yueqi
authors.initials: Y
authors.lastname: Bi
authors.forename: Shengjun
authors.initials: S
authors.lastname: Mao
authors.forename: Liangchun
authors.initials: L
authors.lastname: Gan
authors.forename: Yuanbo
authors.initials: Y
authors.lastname: Li
authors.forename: Changguang
authors.initials: C
authors.lastname: Wang
authors.forename: Nannan
authors.initials: N
authors.lastname: Xu
authors.forename: Yu
authors.initials: Y
authors.lastname: Zheng
authors.forename: Qiuhong
authors.initials: Q
authors.lastname: Cheng
authors.forename: Shixiang
authors.initials: S
authors.lastname: Hou
mesh_terms: D002482:Cellulose / Q000031:analogs & derivatives / Q000737:chemistry; D016503:Drug Delivery Systems / Q000379:methods*; D006863:Hydrogen-Ion Concentration; D007260:Infusion Pumps; D009995:Osmosis; D009997:Osmotic Pressure; D010539:Permeability; D010710:Phosphates / Q000737:chemistry; D010795:Phthalic Acids / Q000737:chemistry; D011092:Polyethylene Glycols / Q000737:chemistry; D016062:Porosity; D012965:Sodium Chloride / Q000737:chemistry; D012995:Solubility; D013608:Tablets, Enteric-Coated / Q000008:administration & dosage / Q000737:chemistry* / Q000493:pharmacokinetics; D013806:Theophylline / Q000008:administration & dosage / Q000737:chemistry* / Q000493:pharmacokinetics; D014665:Vasodilator Agents / Q000008:administration & dosage / Q000737:chemistry* / Q000493:pharmacokinetics
chemical_list: D010710:Phosphates; D010795:Phthalic Acids; D013608:Tablets, Enteric-Coated; D014665:Vasodilator Agents; C005062:acetylcellulose; D011092:Polyethylene Glycols; D012965:Sodium Chloride; D002482:Cellulose; D013806:Theophylline; C018279:sodium phosphate; C007379:diethyl phthalate