"Non-ionic surfactant vesicles as ophtalmic carriers for cyclopentolate. A preliminary evaluation".

The present report deals with a preliminary evaluation of non-ionic surfactant 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 vehicles 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 concentration of components) promoted transcorneal permeation of cyclopentolate with respect to a reference buffer solution, while the opposite effect was observed at pH 7.4. In the pharmacodynamic study, the non-ionic surfactant vesicle formulations, independent of their pH, significantly improved the ocular bioavailability of cyclopentolate, both with respect to reference micellar solutions (i.e., solutions containing only polysorbate 20) and to reference buffer solutions. The contrasting results observed in vitro and in vivo, together with the observed low encapsulation capacity for cyclopentolate of the vesicle formulations, 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 conjunctival and scleral membranes.