Intraocular Safety and Pharmacokinetics of Hexadecyloxypropyl-Cidofovir (HDP-CDV) as a Long-lasting Intravitreal Antiviral Drug

Abstract

To evaluate the intraocular safety and pharmacokinetics of hexadecyloxypropyl-cidofovir (HDP-CDV), the hydrolysis product of HDP-cyclic-CDV, a long-lasting intravitreal cidofovir prodrug for cytomegalovirus (CMV) retinitis. HDP-cyclic-CDV was suspended in phosphate-buffered saline (PBS) at 37°C and formation of HDP-CDV was monitored by high-performance liquid chromatography (HPLC) analysis for 30 weeks. The safety and pharmacokinetics of HDP-CDV intravitreal injections were studied using New Zealand Red rabbits and (14)C labeled HDP-CDV. Ocular tissues from five time points (1, 3, 7, 14, and 35 days) were analyzed by scintillation counting and HPLC to characterize the pharmacokinetics. During the hydrolysis study, approximately 35% of the HDP-cyclic-CDV was converted to HDP-CDV. Evaluation of safety found no toxicity after intravitreal injection of HDP-CDV up to 28 μg/eye. Intravitreal pharmacokinetics of HDP-CDV in the retina, choroid, and vitreous followed a two-phase elimination process and elimination half-lives of 8.4 days (retina), 6.9 days (choroid), and 6.2 days (vitreous). In the retina, cidofovir and an unknown metabolite were detected in the first 2 weeks, and the maximum metabolite concentrations were present 48 hours after the maximum HDP-CDV concentration. HDP-cyclic CDV, under simulated physiologic conditions, slowly converts to HDP-CDV, another potent anti-CMV prodrug that may be taken up by retinal cells and metabolized further to the active antiviral metabolite, cidofovir diphosphate. Taken together, these observations help to explain the ability of a single intravitreal dose of HDP-cyclic-CDV to prevent viral retinitis for up to 68 days in a rabbit model.