Influence of lecithin on some physical chemical properties of poloxamer gels: rheological, microscopic and in vitro permeation studies

Thermoreversible gels may be used in delivery systems which require a sol-g el transition at body temperature. The influence of the addition of lecithi n, a permeation enhancer, on the rheological and in vitro permeation proper ties of poloxamer 407 gels was investigated. Light microscopy and rheologic al parameters were used to characterize the microscopic structure of the fo rmulations which showed non Newtonian behaviour, pseudoplastic flow with a yield value. Increased concentrations of lecithin increased the thixotropy, yield value, apparent viscosity, and the gelation temperature of the gels. Light microscopy showed the formation of micellar structures by the additi on of lecithin, which may account for changes in rheological properties. In vitro permeation of a model drug, triamcinolone acetonide, was decreased w hen the lecithin concentration was increased. The presence of lecithin in t he poloxamer gel improved the characteristics for topical drug delivery. (C ) 1999 Elsevier Science B.V. All rights reserved.