Gellan-based scleral implants of indomethacin: in vitro and in vivo evaluation

Film-type scleral implants of indomethacin with gellan gum were prepared by solvent casting and evaluated for uniformities of thickness, weight, drug content, and surface pH. The effect of plasticizers like glycerol, propylene glycol (PG), and polyethylene glycol 200, and 400 on the void volume of free gellan films (placebo) was calculated from the water content of the films. The drug release from the prepared implants was determined using a static dissolution set-up developed and optimized in our laboratory. Based on the results of the void volume and initial drug release studies, glycerol and PG were selected as the plasticizers for the gellan-based implants. The morphology of the drug-free films (containing 10% and 40% of PG) and the drug-loaded films (before and after dissolution and crosslinked) was studied using scanning electron microscopy. Further, the effect of plasticizer concentration, gellan concentration, effect of crosslinking technique, and duration of crosslinking using calcium chloride on in vitro drug release characteristics were evaluated. Selected batches of the implants were subjected to pharmacodynamic studies, after scleral placement, in uveitis-induced (intravitreal injection of bovine serum albumin 50 microg/ml) rabbit eyes. The release of indomethacin from the prepared implants followed matrix diffusion kinetics with diffusion co-efficient (n) values ranging between 0.358 to 0.708 and seemed to depend on both gellan and plasticizer concentration. Surface crosslinking with 10% calcium chloride for 8 hr retarded drug release (1.42 times less than noncrosslinked implant) and was optimum. The pharmacodynamic studies showed a marked improvement in the various clinical parameters (congestion, keratitis, flare, clot, aqueous cells, and synechias) in the implanted eye compared with the control eye in the rabbits. The scleral implants survived up to 3 weeks in vivo.