Pharmacokinetics of Subconjunctival Liposome-encapsulated Gentamicin in Normal Rabbit Eyes

Subconjunctival injections of antibiotics produce very high corneal levels of drug that fall rapidly as the drug is dissipated. The authors studied the effects of liposome-encapsulation as a means of slowing release from the subconjunctival depot. Liposomes (0.1-1.0 micron) were made of phosphatidic acid, phosphatidylcholine, and alpha-tocopherol. The final suspension contained gentamicin 10 mg/ml with 60-70% encapsulated. Rabbits were given a single subconjunctival injection of liposome-encapsulated gentamicin, gentamicin with "empty" liposomes, or gentamicin alone. In each instance the dose of antibiotic was 5 mg. Gentamicin levels in the sclera and cornea, measured 3,9, and 24 hr after injection, were generally markedly higher with the liposome-encapsulated drug than with the other two preparations. The differences were 5- to 20-fold in the cornea at 24 hr and were statistically significant for temporal cornea. Liposome-encapsulation may be a useful means of extending the effects of a subconjunctival injection of antibiotic.