Interaction of a nonionic surfactant-based organogel with aqueous media

In an attempt to explain the rather short half-life of molecules at the injection site after their intra-muscular administration in a sorbitan monostearate organogel, in vitro studies were carried out to study the effects of an aqueous medium (simulating interstitial fluid at injection site) on the physical form of the organogel. When the gel mass comes in contact with an aqueous phase, the latter penetrates into the organic gel via the sorbitan monostearate tubular network, resulting in gel breakdown into smaller fragments. The surfactant tubular network act as a conduit for water penetration into the gel. Meanwhile, emulsification, aided by the surfactants present in the gel, also occurs at the gel surface between the organogel and the aqueous phase. This leads to a gradual erosion of the gel as oil droplets bud off from the gel mass. From these in vitro observations, we speculate that after gel administration in vivo, dynamic interactions occur between the local interstitial fluid and the gel mass: fluid penetration into the gel and emulsification at the gel surface is thus responsible for gel breakdown and so a relatively short duration of drug at the injection site.