Retinal delivery of celecoxib is several-fold higher following subconjunctival administration compared to systemic administration

Purpose. We have previously demonstrated that celecoxib, a selective COX-2 inhibitor, reaches the retina following repeated oral administrations and inhibits diabetes-induced vascular endothelial growth factor (VEGF) mRNA expression and vascular leakage in a rat model. The aim of this study was to quantify the relative retinal bioavailability of celecoxib from the subconjunctival route compared to a systemic route. Methods. The plasma and ocular tissue distribution of celecoxib was determined in male Sprague-Dawley rats following subconjunctival and intraperitoneal administrations of drug suspension at a dose of 3 mg/rat. The animals were sacrificed at 0.5, 1, 2, 3, 4, 8, and 12 h post-dosing, the blood was collected, and the eyes were enucleated and frozen. The plasma, sclera, retina, vitreous, lens, and the cornea were isolated and celecoxib levels were determined using an HPLC method. The tissue exposure of the drug was measured as the area under the curve (AUC(0-infinity)) of the concentration vs. time profiles. The relative bioavailability was estimated as the AUC(0-infinity) ratio between subconjunctival and intraperitoneal groups. Results. For the subconjunctivally dosed (ipsilateral) eye, the AUC(0-infinity) ratios between subconjunctival and intraperitoneal groups were 0.8 +/- 0.1, 53 +/- 4, 54 +/- 8, 145 +/- 21, 61 +/- 16, and 52 +/- 6 for plasma, sclera, retina, vitreous, lens, and cornea, respectively. For the contralateral ocular tissues, the AUC(0-infinity) ratios were 1.2 infinity 0.3, 1.1 infinity 0.3, 1.1 +/- 0.4, 1.0 +/- 0.3, and 1.2 +/- 0.3 in the sclera, retina, vitreous, lens, and the cornea, respectively, between the subconjunctival and the intraperitoneal groups. Assuming that the drug AUCs in contralateral eye were equal to the systemic pathway contribution to AUCs in the ipsilateral eye, the percent contribution of local pathways as opposed to systemic circulation for celecoxib delivery to the ipsilateral eye tissues was estimated to be 98% or greater. Conclusions. The retinal delivery of celecoxib was substantially higher following subconjunctival administration compared to the intraperitoneal route. The transscleral pathway almost completely accounts for the retinal celecoxib delivery following subconjunctival administration.