Metabolic profiles of difluprednate in rabbit ocular tissues after instillation of difluprednate ophthalmic emulsion.

Difluprednate (DFBA; 6alpha,9-difluoro-11beta,17,21-trihydroxy-1,4-pregnadiene-3,20-dione 21-acetate 17-butyrate) is an effective anti-inflammatory agent derived from prednisolone. The present study aimed to evaluate the metabolite profile of DFBA in rabbit ocular tissues after instillation of DFBA ophthalmic emulsion. The high-performance liquid chromatography with radiochemical detection was employed to analyze radioactivity in rabbit ocular tissues that had been instilled with a (3)H-DFBA 0.05% ophthalmic emulsion. At 0.5 and 2 h after instillation, DFBA was not detected in the cornea, aqueous humor, or iris/ciliary body. Instead, 21-deacetylated DFBA (DFB), 17-debutylated DFB (DF), and an unknown metabolite were found. The unknown metabolite was identified as de-17-side chain-glucocorticoid metabolite (DF21C), which is a novel glucocorticoid metabolite formed by the scission of the 17-side chain via an unknown metabolic reaction pathway. The K(i) value of DF21C was 5.6 x 10(-7) mol/L, indicating very weak glucocorticoid receptor binding of DF21C (approximately 1000-fold less than that of DFBA and DFB).