NONIONIC SURFACTANT VESICLES AS OPHTHALMIC CARRIERS FOR CYCLOPENTOLATE - A PRELIMINARY EVALUATION

The present report deals with a preliminary evaluation of non-ionic su rfactant vesicles as ocular vehicles for cyclopentolate. The vesicles were obtained by sonication of equimolar mixtures (either 75 or 15 mM) of polysorbate 20 and cholesterol. Non-ionic surfactant vesicle vehic les containing cyclopentolate (0.5 or 1.0% w/v) and buffered at two pH values (7.4 and 5.5) as well as appropriate reference solutions were tested for cyclopentolate permeation through rabbit corneas in vitro, and for mydriatic activity in rabbits. In the in vitro study, the pH 5 .5 non-ionic surfactant vesicle formations (independent of the molar c oncentration of components) promoted transcorneal permeation of cyclop entolate with respect to a reference buffer solution, while the opposi te effect was observed at pH 7.4. In the pharmacodynamic study, the no n-ionic surfactant vesicle formulations, independent of their pH, sign ificantly improved the ocular bioavailability of cyclopentolate, both with respect to reference micellar solutions (i.e., solutions containi ng only polysorbate 20) and to reference buffer solutions. The contras ting results observed in vitro and in vivo, together with the observed low encapsulation capacity for cyclopentolate of the vesicle formulat ions, led the authors to formulate the provisional hypothesis that non -ionic surfactant vesicles may promote absorption of cyclopentolate by preferentially modifying the permeability characteristics of the conj unctival and scleral membranes.