Effect of propylene glycol on in vitro membrane transport of ionized diclofenac diethylamine from saturated binary cosolvent mixtures

For saturated formulations, where thermodynamic activity () is equal to 1, the flux of the permeant through a membrane should theoretically be constant irrespective of the delivery vehicle (Higuchi 1960). Although some studies have supported this hypothesis for saturated binary mixtures of propylene glycol (PG)/ water (e.g. Twist and Zatz 1986), variations from this ideal behaviour have been reported (e.g. Pellett et al 1994). Therefore, no definitive conclusions have been made regarding the influence of PG on the membrane transport rate of drugs from saturated vehicles. The aim of this study was to investigate systematically the impact of PG on the permeation of one drug, diclofenac diethylamine (DDEA), from a series of saturated binary mixtures, through model membranes.