Sustained release of liposome-encapsulated enrofloxacin after intramuscular administration in rabbits.

Enrofloxacin was encapsulated in multilamellar liposomes composed of phosphatidylcholine and cholesterol (molar ratio, 1:1), and its potential use as sustained release formulation was evaluated. The encapsulated drug was administered IM to rabbits (n = 6). Results indicated that absorption rate was slow, compared with previous studies; additionally, peak concentration was lower (0.5 +/- 0.1 microgram/ml), and the time to peak concentration was considerably longer for liposome-encapsulated enrofloxacin (1.5 +/- 1.08 hours) than for unencapsulated drug. Apparent elimination half-life of drug in the body was significantly (P < 0.05) increased (4.05 +/- 1.08 hours) when it was administered encapsulated in liposomes. Large-size liposomes containing enrofloxacin administered IM to rabbits gave sustained drug release from the injection site, providing therapeutic and prolonged plasma concentrations of drug in the body.