EFFECT OF NONIONIC SURFACTANT ON TRANSPORT OF MODEL-DRUGS IN EMULSIONS

Purpose. To investigate the influence of excess surfactant on transpor t kinetics in emulsions, using phenylazoaniline (PAA), benzocaine, ben zoic acid and phenol as model drugs. Mineral oil was chosen as the oil phase and the nonionic surfactant, polyoxyethylene oleyl ether (Brij 97) as the emulsifier. Methods. Model drug transport in emulsions was investigated using side by side diffusion cells mounted with hydrophil ic dialysis or hydrophobic membranes. A novel method, involving a comb ination of a membrane equilibrium technique and surface tension measur ement (Wilhelmy plate method), was developed to determine surfactant c ritical micelle concentration (CMC) in the presence of O/W emulsions. Emulsion stability was determined by droplet size analysis as a functi on of time, temperature and dilution using photon correlation spectros copy and a light blockage technique. Model drug mineral oil/water part ition coefficients and aqueous solubilities were determined in the pre sence of surfactant. Results. The emulsion CMC value was used to calcu late micellar phase concentration. The transport rates of PAA and benz ocaine in emulsions increased with increase in Brij 97 micellar concen tration up to 1.0 % w/v and then decreased at higher surfactant concen trations. The transport rates of the more hydrophilic compounds, benzo ic acid (ionized form, pH 7.0) and phenol, were not affected by the pr esence of micellar phase. Conclusions. Excess surfactant affected the transport rates of the model drugs in the emulsions depending on drug lipophilicity. Transport rates measured using side by side diffusion c ells appeared to be governed by model drug partitioning rates from the oil to the continuous phases and by membrane type.