By virtue of the biocompatibility of their constituent phospholipids and of their ability to influence cell membrane permeability, liposomes are an attractive system for topical ocular drug delivery. The objective of this study was to investigate whether the ocular disposition of epinephrine and inulin in the albino rabbit was similarly affected following their encapsulation in multilamellar liposomes. Drug concentrations in tears, conjunctiva, cornea, iris plus ciliary body and aqueous humor were monitored at 30 min post-instillation of various preparations of each drug using radiotracer techniques. Liposomal drug entrapment was found to have opposite effects on the corneal and conjunctival absorption of epinephrine and inulin, epinephrine absorption was reduced by 50% whereas inulin absorption was increased 10 times. Quite unexpectedly, although inulin was detected in the uveal tract, none of it was detected in the aqueous humor when presented in liposomal form. These preliminary data suggest that while the corneal and conjunctival absorption of a drug can be modified by its entrapment in liposomes, its disposition in the intraocular tissues is unlikely to be controlled entirely by liposomes, since few, if any, of the liposomes that may be absorbed are expected to maintain their integrity while permeating the cornea.
ASJC Scopus subject areas
- Pharmaceutical Science