Development and characterization of poly (D, L-lactide-co-glycolide) based sustained release formulation of ganciclovir in treatment of cytomegalovirus retinitis

Human cytomegalovirus (HCMV) retinitis is a serious sight threatening disease affecting immunocompromised individuals such as acquired immuno deficiency syndrome patients with CD4 cell counts less than 50 cells/mul. Ganciclovir was the first anti-HCMV drug approved by Food and Drug Administration for disease management. Owing to its virustatic properties, indefinite maintenance of ganciclovir levels in retina is necessary to prevent disease progression. Previously, management of retinitis with ganciclovir was two fold with induction and maintenance therapy via daily infusions. Systemic toxicity with such infusions prompted the development of local ganciclovir therapy by direct intravitreal administration and sustained delivery by non-biodegradable implants.; Primary focus of this research is the development and evaluation of a biodegradable sustained-release formulation of ganciclovir for intravitreal administration in the management of HCMV retinitis. Two strategies that are employed to develop the formulation include polymer blending in preparation of ganciclovir loaded poly(D,L-lactide-co-glycolide) (PLGA) microspheres and physical mixing of microspheres prepared from different PLGA polymers for attaining constant ganciclovir release for required time periods.; Polymer blending, mixture of two different grades of PLGA molecules, was employed in preparation of ganciclovir loaded microspheres for modulating drug release. Polymer blending was effective in modulating ganciclovir release from the microspheres from 5--90 days depending on the blend employed for preparation. Novel formulations were developed by dispersing microspheres in thermogelling PLGA and polyethylene glycol triblock copolymer solution and release of ganciclovir from the formulations was studied. Formulations with ganciclovir release over 3--4 weeks by microsphere mixing were prepared and evaluated in conscious rabbit microdialysis model with permanently implanted vitreous probe. Therapeutic levels of ganciclovir were maintained by the formulation for 14 days upon intravitreal administration relsative to 2.5 days following administration of standard GCV injection.; In another study, expression and role efflux proteins was investigated in controlling ocular absorption and elimination of their substrate, quinidine, across blood ocular barriers. Studies reveal that efflux proteins inhibit the entry of their substrates into neural retina from both systemic circulation and vitreous to maintain tissue homeostasis. Inhibition of these proteins can cause 1.5--2 fold increase in retinal concentrations upon systemic drug administration.