Effect of cationic surfactant on transport of model drugs in emulsion systems.

Excess surfactant present in emulsions can influence the rates of transport of incorporated drugs by micellar solubilization, alteration of the partitioning process and by drug-surfactant complexation. Cetyltrimethylammonium bromide (CTAB), a cationic surfactant was selected to investigate these phenomena as it forms relatively stable mineral oil-water (O-W) emulsions and has the potential for ionic interaction. Phenylazoaniline, benzocaine, benzoic acid and phenol were chosen as model drugs for this study. The emulsion critical micelle concentration (CMC) for CTAB determined using a combination of a membrane equilibrium technique and surface-tension measurement was 1.0% w/v in 10% v/v% O-W emulsion systems. Ionic interaction between model drugs and surfactants and drug hydrophobicity affected their transport rates in the emulsion systems. The transport rates of the lipophilic drugs (benzocaine and phenylazoaniline) and the ionized hydrophillic drug (benzoic acid, pH 7.0) in the emulsion systems increased with increasing CTAB concentration up to 0.5% w/v micellar concentration and then decreased at higher concentrations. The rate of transport of phenol was not affected by the presence of micellar phase. Ionic interaction between surfactant and model drugs affected transport rates of model drugs in emulsion systems. The micellar phase was considered to affect the overall transport rates of model drugs.