Effect of the amphoteric properties of salbutamol on its release rate through a polypropylene control membrane.
The permeation of salbutamol from aqueous vehicles with different pH values through the Celgard 2500 polypropylene membrane was studied, the goal being to assess the effect of the amphoteric properties of the drug on its release by the membrane. Permeation rates were generally low, which was related to the fact that purely aqueous vehicles were not imbibed into the pores of the membrane and therefore permeation took place through the amorphous polypropylene domains. Permeability coefficients were not proportional to the fraction of uncharged drug at different bulk pH values, indicating that either a pH gradient between the bulk and the membrane surface exists and/or charged drug species can permeate the hydrophobic membrane. Calculated hypothetical pH values of the membrane surface, assuming permeation of the uncharged drug only, failed to provide a consistent explanation of the experimental permeabilities. Permeability coefficients of the different ionization forms of the drug assuming no pH gradient were calculated from a system of linear equations, each one of them corresponding to a specific bulk pH. These were for the anionic and the cationic species one to two orders of magnitude smaller than for the combined uncharged and zwitterionic species. It is possible that both, a pH difference between bulk and membrane surface and permeation of ionized molecules were simultaneously responsible for the observed permeation rates.
Imboden
R
R
University of Basel, Switzerland.
Imanidis
G
G
D000420:Albuterol / Q000008:administration & dosage* / Q000737:chemistry; D016503:Drug Delivery Systems; D006863:Hydrogen-Ion Concentration; D010539:Permeability; D011126:Polypropylenes / Q000008:administration & dosage*; D012995:Solubility; D013566:Sympathomimetics / Q000008:administration & dosage*
D011126:Polypropylenes; D013566:Sympathomimetics; D000420:Albuterol