Corticosteroid intravitreal implants

Abstract

Intraocular implants developed for ocular inflammation which release glucocorticoids for a prolonged period within the vitreous cavity make use of either a bioerodible polymer (dexamethasone in polylactic acid-coglycolic acid matrix) or non-erodible implantable device (fluocinolone acetonide, FA, in a polyvinyl acetate/silicone laminate). Pharmacologically, both steroids are similar in their binding characteristics to glucocorticoid receptors (GR), their ability to transactivate the GR complex and their vitreous half-lives. They both possess neuroprotective properties for retina and retinal pigment epithelium which place them apart from triamcinolone acetonide. Triamcinolone acetonide's higher lipophilicity makes it possible to create an implant with prolonged release characteristics, but may be increasing the propensity for ocular side effects such as cataract and glaucoma. In clinical trials, both implants were shown to be effective at inhibiting intraocular inflammation in patients with intermediate or posterior uveitis. The Dexamethasone implant is inserted through a 22-gauge needle through the pars plana and can control inflammation for up to 6 months. The FA implant requires surgical insertion through the pars plana and can control inflammation for up to 3 years. The MUST trial has shown the FA implant when placed bilaterally to be slightly more effective than strict systemic therapy, though at the cost of additional ocular surgeries for cataract and glaucoma. Certain clinical situations particularly with asymmetric uveitis may in fact favor local vs. systemic therapy.