Influence of the Viscosity and the Surface Tension of Ophthalmic Vehicles on the Retention of a Tracer in the Precorneal Area of Human Eyes

Abstract

Multidose eye drops packages contain preservatives as required by the pharmacopoeiae. Most of the commonly used preservatives exhibit surface activity and they may disrupt the superficial lipid layer of the tear film. Consequently surfactants may have a negative influence on the tear film stability, the blinking rate and the wash out of a therapeutic agent instilled. The aim of the present word is to examine the influence of the surface tension of ophthalmic solutions on the retention of fluorescein in the precorneal area of human eyes. The elimination is measured by monitoring the fluorescein decay in the tearfilm with a slit lamp fluorophotometer. Because of the cytotoxicity of most preservatives, a nonirritant non-ionic surfactant (tween 80) is selected. Several concentrations of surfactant related to its CMC and to the usual surface tension of ophthalmic solutions are examined. The addition of po]ysorbate 80 to 0,9% NaCI + 0,1% Na fluorescein solutions does not seem to influence the decay profile of the tracer, except at the highest concentration of 0,01% tween 80. The subjects complain of mild irritation, starting a few minutes after instillation. The rate constant (k) for the disappearance of fluorescein was calculated. The k va]ues obtained indicate a faster elimination when the concentration of the surfactant in the vehic1~ increases. The analysis of variance reveals, however, no ~tatistically differences (P < 0,05). The results appear to indicate that a non-ionic surfactant does not influence the elimination of a drug if the concentration used does not elicit irritation or lacrimation.Dept. Pharmaceutical Sciences, University of Antwerp (UIA). Universiteitsplein 1 -B-2610 Wilrijk Antwerpen. delivery. This requires the rate limiting barrier to be in the creams rather than in the skin. To achieve this aim a dual strategy is being followed: I. by using the capacity of cream components to enhance the permeability of the skin 2. by using the colloidal gel structures to control the drug release rate.This study specifically deals with the relationship between cream structures end drug release "in vitro". Drug release experiments were performed in order to characterize the drug diffusion in relation to the gelstructure of the creams and the lipophilicit'Y of the drug. Creams were prepared by mixing Brij96R (polyoxyethylene( 10)-oleglether, a nonionic surfactant) and water. Depending on the mixing ratio they can adopt a lamellar, or a hexagonal gelstructure, while in some cases a viscous isotropic gelstructure is present. The model drugs (esters of p-aminohenzoic acid) were solubilized (i%) in the creams without disturbing the gelstructures as verified by small angle X-ray scattering (SAXS).Results and discussion:In the lamellar end hexagonal creams the.effective diffusion coefficient of benzocaine increased gradually with the water content due to a volume increase of the hydrophilic domains of the creams, that form the continuous phase. In the viscous isotropic creams %J~e diffusion of benzocaine was relatively ...

Improving ultrasound gene transfection efficiency by controlling ultrasound excitation of microbubbles

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Challenges and opportunities in polymer technology applied to veterinary medicine

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Eye drop container delivery: a source of response variation?

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