Abstract
Background: The poor bioavailability of ophthalmic drops is mainly due to the rapid nasolacrimal drainage of the drug and very low permeability of corneal epithelium. Hence, there is an interest to find an effective system to improve drug permeability and bioavailability. Objectives: The aim of the present study was to design and characterize a novel microemulsion system as an ocular delivery system for Azithromycin and evaluate its physicochemical characteristics and rabbit corneal permeability in order to enhance the penetration of the drug. Methods: The prepared microemulsions (MEs) were assessed for their viscosity, pH, particle size, surface tension, DSC, stability, in vitro drug release, and corneal rabbit permeability. In this study, a full factorial design was employed with 3 variables at 2 levels for preparing 8 formulations and data analysis. Results: The results showed that the average droplet size of ME formulations was in the range of 6.78 to 26.65 nm while pH values were 5.1 to 5.7 and viscosity range was 115 - 361 cps. Drug release profile revealed that 79.066% of the drug released in 24 hours of the experiment. The maximum and minimum percentages of drug permeated through rabbit cornea were observed in MEA-7 (12.87%) and MEA-2 (0.909%), respectively. All ME formulations with different compositions and properties significantly increased partitioning, flux, and permeability coefficient from rabbit cornea. Dapp and Papp parameters in MEA-1 and MEA-7 formulations were 0.00882 cm2h-1 and 2.391 cmh-1, which were 17.65, 35.17 times higher than those of control (AZ suspension, 1%), respectively. The flux (Jss) of Azithromycin in MEA-7 was 11.958 mg cm-2h-1, which was 39.86 times higher than that of control. Conclusions: The present study showed that any change in the content and composition of ME could change physicochemical properties and permeability parameters during drug permeation of ME formulations. The phenomenon may be due to the cornea structural changes in presence of ME components.
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