Relevance of polymer molecular weight to the in vitro/in vivo performances of ocular inserts based on poly(ethylene oxide)

A previous study of the present authors on gel-forming erodible inserts, based on high molecular weight (MW, 400 kDa) poly(ethylene oxide) (PEO), for ocular controlled delivery of ofloxacin (OFX) has been extended to investigate the effects of PEO MW, in the 200-2000 kDa range, on insert properties relevant to therapeutic efficacy. Mucoadhesion has shown a dependence on MW, with a maximum for PEO 400. The in vitro drug release from inserts based on PEO 200, PEO 400 and PEO 900 was mainly controlled by insert erosion, whereas with PEO 2000 it was mainly diffusion-controlled in a first phase, followed by an erosion-controlled phase. The erosion time scale depended directly on MW. Immediately after application in the lower conjunctival sac of the rabbit eye, the inserts: based on PEO of whichever MW formed mucoadhesive gels, well tolerated by the animals: then the gels spread over the corneal surface and eroded. PEO 2000 was unsuitable as an insert material, since the resulting gel spilled from the eye, due to excessive swelling. The gel residence time in the precorneal area. the drug permanence time in the aqueous humor at concentrations > MIC and the time to reach the maximal drug concentration in the aqueous humor (C-max) depended directly on MW, indicating that transcorneal absorption was governed by gel erosion. All inserts increased C-max and AUG(eff) (AUC for concentrations > MIC) with respect to the commercial eyedrops. The increases caused by PEO 400 and PEO 900 were similar (3.78- and 3.16-fold, respectively, for C-max; 11.06- and 12.37-fold, respectively, for AUC(eff)), whereas smaller increases were produced by PEO 200. The PEO 400 and PEO 900 inserts have shown a potential for a topical treatment of endophthalmitis. (C) 2001 Elsevier Science B.V. All rights reserved.