A gamma scintigraphic evaluation of the precorneal residence of liposomal formulations in the rabbit.

Multilamellar liposomes were prepared from dipalmitoyl phosphatidylcholine or egg lecithin in combination with cholesterol and either dicetyl phosphate or stearylamine. The size and charge of the colloidal preparations were characterized before labelling with [111In]8-hydroxyquinoline. Freshly labelled liposomes were instilled into the eyes of unanaesthetized NZW rabbits and their disposition and drainage followed using gamma scintigraphy. A positive surface charge was found to affect significantly liposomal drainage rate, whereas an increase in size restricted drainage from the inner canthal region. Drainage of the suspending medium was directly compared with liposomes by labelling the medium with [99mTc] sodium pertechnetate and following the simultaneous change in removal of 99mTc and 111In from the precorneal area. Slower drainage rates were obtained for the suspending medium compared with solutions of the isotopes suggesting that the liposomes restricted solution drainage.