phase transition temperature.

To increase the low bioavailability and short ocular residence time of lomefloxacin eye drops, aqueous solutions of drug in chitosan/ Pluronic (poloxamer) were prepared to identify suitable compositions with regard to gel forming properties and drug release behaviour. Mixtures of solutions of Pluronic (10-25% w/w) with chitosan (0.1-0.3% w/w) of different molecular weights (Mw) were prepared. Lomefloxacin release was determined using a membrane less dissolution model in artificial tear solution up to 8 hours and the samples were analyzed spectrophotometrically at 281nm. The rheological behaviour of solutions in response to dilution or temperature changes and also the phase change temperature (PCT) were determined using a brookfield’s viscometer. Antimicrobial effect of the solutions was studied in nutrient agar using Staphylococcus aureus by using agar well diffusion method. The formulation consisted of 15% Pluronic and 0.1% low Mw chitosan, with the highest release efficiency (41.952 %) , is suggested as a suitable ophthalmic preparation for sustained release of lomefloxacin HCl. It was liquid in non-physiologic conditions (pH 4 and 25ºC) and transferred to the gel form upon physiologic conditions (pH 7.4 and 37ºC). The PCT of this in situ gel did not change upon dilution.