Purpose: Topical tacrolimus is currently used in ocular surface pathologies as a corticosteroid-sparing immunosuppressive agent. It could also help prevent endothelial corneal graft rejection and inflammatory diseases; however, its hydrophobic nature and high molecular weight theoretically limit its intraocular penetration. The aim of this study is to investigate the corneal and intraocular penetration of a 0.1% tacrolimus ophthalmic suspension. Methods: Sixteen rabbits were randomly spread into four groups defined by the delay between the last tacrolimus instillation and corneal sampling (2, 6, 11, and 24 h). Three rabbits per group received bilateral instillations of tacrolimus twice daily for 5 days, the 4th subject in each group serving as negative controls. The 5th day, conjunctiva, corneal epithelium, anterior stroma, posterior stroma, corneal endothelium, iris, choroid/retina, aqueous humor, and plasma samples were collected. Tacrolimus concentrations were determined using high-performance liquid chromatography coupled with tandem mass spectrometry. Results: Maximum mean concentration was reached after 2 h in the epithelium, anterior and posterior stroma, and endothelium: 12794 (±2656), 436 (±178), 341 (±179), and 4125 (±1673) ng/g, respectively. The descending rank order of exposure over 24 h was: corneal epithelium; corneal endothelium; conjunctiva; anterior stroma; posterior stroma; iris; and chorioretina with 158.0; 39.99; 4.620; 4.134; 3.350; 0.384; 0.270 ng.h/mg, respectively. Conclusions: Tacrolimus concentrations measured in the corneal tissues are significantly higher than that described as lower limit of efficacy in solid organ transplantation. Topical 0.1% tacrolimus could therefore become an alternative to corticosteroids for endothelial graft rejection prevention and endothelial inflammatory pathologies management.
Keywords: cornea; drug delivery; drug penetration; keratoplasty; pharmacokinetics; tacrolimus.