Carrageenan-gelatin mucoadhesive systems for ion-exchange based ophthalmic delivery: in vitro and preliminary in vivo studies.

Lambda-carrageenan is an anionic polymer able to ionically interact with alkaline drugs. This results in a complex that releases the drug slowly, due to displacement by the counterions of the release medium. The aim of this work was to assess the possible ophthalmic employment of such a complex. As a model drug, an alkaline anti-glaucoma drug, timolol maleate, was chosen. Systems in which lambda-carrageenan interacted both with the drug and a mucoadhesive polymer such as gelatin were studied. The combination of carrageenan and gelatin in different ratios proved to be useful in modulating the drug release profiles, the rheological properties of the hydrated formulations and their mucoadhesive properties. Both films and microspheres were prepared and tested in vitro. A microsphere formulation was also tested in vivo in albino rabbits. The drug concentration and bioavailability in the aqueous humour were significantly high in comparison with commercial formulations.