Interaction of a nonionic surfactant-based organogel with aqueous media

In an attempt to explain the rather short half-life of molecules at the inj ection site after their intra-muscular administration in a sorbitan monoste arate 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 fragm ents. 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 aq ueous 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 l ocal interstitial fluid and the gel mass: fluid penetration into the gel an d emulsification at the gel surface is thus responsible for gel breakdown a nd so a relatively short duration of drug at the injection site. (C) 1999 p ublished by Elsevier Science B.V. All rights reserved.