Multivesicular liposomes for sustained release of naltrexone hydrochloride: design, characterization and in vitro/in vivo evaluation.

Multivesicular liposomes containing naltrexone hydrochloride (DepoNTX) was prepared by using the traditional DepoFoam technology and the key formulation factors on encapsulation efficiency and particle size were investigated. A morphological characterization and in vitro/in vivo release assay was also carried out. NTX was successfully encapsulated in DepoNTX with good yield and showing the spherical, smooth and multivesicular characteristics of particle by a light microscope. The in vitro studies in human plasma and sodium chloride showed that 80-85% of NTX encapsulated in MVLs released slowly from particles over 5 days. In vivo study, after a single dose of 2.0 mg/kg of DepoNTX formulation administered subcutaneously in rats, plasma NTX levels were maintained at a relatively constant level above 10 ng/mL for approximately 120 h, while after administered NTX solution, NTX level was quickly decreased below 10 ng/mL within 20 h. The results of the study demonstrated that DepoNTX was very promising candidate for sustained release delivery of naltrexone hydrochloride.