Abstract
Difluprednate is a synthetic glucocorticoid used for the treatment of postoperative inflammation and pain associated with endogenous uveitis. It is very lipophilic with limited aqueous solubility and stability. The only available marketed formulation is an oil-in-water ophthalmic emulsion that has many drawbacks. Cyclodextrin (CD) molecules are widely used to increase the solubility and stability of hydrophobic drugs through the formation of drug/CD complexes. This study aims to investigate degradation kinetics, stability and solubility of difluprednate in aqueous CD solutions in an effort to develop aqueous eye drop vehicle for ophthalmic delivery. Phase-solubility and kinetics studies were performed in presence of different CDs and polymers. Characterization of the drug/CD complexes was done using techniques like NMR, DSC, and FTIR. The results show that difluprednate has maximum stability at pH 5 in aqueous CD solution. HPγCD was found to be the best solubilizer and stabilizer among all the CDs tested. The stability was further improved with the combination of HPγCD and different polymers. Characterization of the difluprednate/HPγCD complex in solid and solution state confirmed the presence of a drug/CD complex. It was possible to solubilize 0.1% difluprednate using HPγCD and stabilize the drug using combination of CD and polymer in aqueous solution.
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