PH OF PREPARATIONS AFFECTING THE ON-OFF DRUG PENETRATION BEHAVIOR THROUGH THE THERMORESPONSIVE LIQUID CRYSTAL-EMBEDDED MEMBRANE

A liquid crystal (cholesteryl oleyl carbonate, COC)-embedded membrane with a controlled rate and higher reversibly thermo-responsive functio n was successfully fabricated by the vacuum filtration method. The aim of this study was to investigate the effect of the pH of aqueous solu tions and gel preparations on the penetration of salbutamol sulfate th rough this thermo-responsive COC-embedded membrane. The results indica te that the on-off switching penetration behavior of salbutamol sulfat e through the COC-embedded membrane in response to a repeatedly exchan ging temperature cycle (10 double left right arrow 25 degrees C) is no t influenced by the pH of the medium. However, the pH-dependent ioniza tion of salbutamol and the viscosity of the gel base, as well as the i nteraction between salbutamol and carbopol, might change the amount an d the rate of salbutamol sulfate that penetrates across this COC-embed ded membrane. (C) 1998 Elsevier Science B.V.