Distribution of liposome-incorporated carboxyfluorescein in rabbit eyes

The penetration of liposomal drugs into rabbit eyes was investigated using 6-carboxyfluorescein (6-CF) as a water-soluble model substance. It was possible to incorporate 4.1 mg 6-CF into the aqueous space of 1 ml of liposomes produced with reverse phase technique. In comparison to aqueous 6-CF, liposomal 6-CF reached extremely high concentrations in all parts of the eye, and was released slowly over many days. The highest concentration of liposomal 6-CF (55 micrograms g-1) was found in the sclera 30 minutes after injection. The corresponding value of aqueous 6-CF was 5 micrograms g-1. After 7 days, liposomal 6-CF was still detectable at the subconjunctival injection location as well as in the sclera, retina, chorioid and cornea. In clinical examination and fluorescence photography no side effects were observed except for moderate and transitory conjunctivitis. In conclusion, liposomes are appropriate drug carriers for delivery of drugs to the posterior eye segment. This method is, however, limited to drugs with chemical properties which permit incorporation in pharmacologically relevant amounts.