title: Formulation of hydrophilic non-aqueous gel: drug stability in different solvents and rheological behavior of gel matrices.
abstract: OBJECTIVE
  This study was aimed at formulating a hydrophilic non-aqueous gel for topical delivery of the model moisture-sensitive drug, minocycline hydrochloride (MH).
  
  
  METHODS
  Stability study of MH dissolved in water and various hydrophilic non-aqueous solvents was performed over a period of four months in order to select a suitable non-aqueous solvent for MH gel. To improve MH stability, the effect of different cation additives on MH stability in the selected solvent was investigated. Non-aqueous gel matrices were prepared from three different types of hydrophilic polymers in glycerin-propylene glycol mixture with Mg(2+) cation additive. Oscillatory shear rheometry was performed on the gel matrices using a cone-and-plate rheometer.
  
  
  RESULTS
  MH stability was affected by the type of solvent employed and the duration of storage. Different cation additives affected the extent of MH stabilization through MH-cation complex formation. Rheological properties of the non-aqueous gel matrices were significantly affected by the type and concentration of polymer, and the vehicle ratios in the formulations.
  
  
  CONCLUSIONS
  MH stabilization could be achieved using the selected glycerin-propylene glycol mixture containing MgCl(2). Gel matrix formulated using this solvent system and 3%w/w N-vinylacetamide/sodium acrylate copolymer had demonstrated the most favorable rheological properties as a gel for topical application.
authors.affiliation: Department of Pharmacy, Faculty of Science, National University of Singapore, Singapore. keatchow@uts.cc.utexas.edu
authors.forename: Keat Theng
authors.initials: KT
authors.lastname: Chow
authors.forename: Lai Wah
authors.initials: LW
authors.lastname: Chan
authors.forename: Paul W S
authors.initials: PW
authors.lastname: Heng
mesh_terms: D000287:Administration, Topical; D000900:Anti-Bacterial Agents / Q000008:administration & dosage* / Q000737:chemistry*; D002412:Cations / Q000737:chemistry; D002626:Chemistry, Pharmaceutical; D002851:Chromatography, High Pressure Liquid; D016503:Drug Delivery Systems; D004355:Drug Stability; D005782:Gels; D008911:Minocycline / Q000008:administration & dosage* / Q000737:chemistry*; D012212:Rheology; D012997:Solvents; D014783:Viscosity; D014867:Water / Q000737:chemistry
chemical_list: D000900:Anti-Bacterial Agents; D002412:Cations; D005782:Gels; D012997:Solvents; D014867:Water; D008911:Minocycline