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The purpose of this research was to optimize the formulation factors for maximum in vitro permeation of gatifloxacin from aqueous drops through excised goat cornea and to evaluate the permeation characteristics of drug from selected marketed eyedrop formulations. Permeation studies were conducted by putting 1 mL of formulation on the cornea (0.67 cm2) fixed between the donor and receptor compartments of an all-glass modified Franz diffusion cell and measuring gatifloxacin concentration in the receptor (containing normal saline under stirring) by spectrophotometry at 291.5 nm, after 120 minutes. Raising the drug concentration of the drops increased the drug permeation but decreased the percent permeation and the in vitro ocular availability. Raising the pH of the formulation from pH 5 to 7.2 increased both the drug permeation and the in vitro ocular availability. Eyedrops containing benzalkonium chloride (BAK; 0.01% wt/vol) and disodium edetate (EDTA; 0.01% wt/vol) showed maximum permeation, followed by Zymar, BAK (0.01% wt/vol), Gatilox, Gatiquin, and Gate (statistically significantP<.05 compared with control). In vitro titration of the formulations with 0.1N NaOH indicated the presence of a buffer in Zymar (pH 6) and Gate (pH 5.8), which may cause irritation and induce lacrimation, resulting in reduced ocular availability in vivo. Thus, formulation with BAK and EDTA, which is unbuffered, has a better likelihood of being absorbed in vivo. The BAK-EDTA formulation significantly (P<.05) increased the permeation of gatifloxacin through paired excised corneas of goat, sheep, and buffalo, compared with the control formulation. The goat cornea showed the greatest increase in permeation, followed by the sheep and buffalo corneas.