A novel method to prepare highly encapsulated interferon-alpha-2b containing liposomes for intramuscular sustained release.

A novel modified film-hydration-dilution method was employed to prepare highly encapsulated interferon-alpha-2b containing liposomes for intramuscular sustained release. The liposomes produced by this technique were a mixture of mainly unilamellar vesicles and a small number of multilamellar vesicles. The trapping efficiency was above 80%. With at least 60-fold dilution, Triton X-100 at the concentration of 0.3% (w/v) in phosphate buffered saline (PBS) was able to solubilize phospholipids without denaturing the protein and/or interfering with the enzyme-linked immunoassay (ELISA). After three homogenization cycles under a pressure of 70 MPa the size of liposomes was reduced from 978 to 101 nm while the activity of interferon-alpha-2b decreased by 9.9% compared to the control. Although liposomes were physically stable for 22 months at 4 degrees C the mean size of the liposomes increased slightly from 101 to 122 nm. The levels of free interferon-alpha-2b at the site of intramuscular injection decreased rapidly with only 4.15% of initial dose retained at the injection site after 0.33 h following injection of an interferon-alpha-2b solution (nonencapsulated). In contrast, interferon-alpha-2b encapsulated in liposomes was retained at the site of intramuscular injection at higher levels than free interferon-alpha-2b (p < 0.05). Larger liposomes containing interferon-alpha-2b (978 nm) were the most effective for local retention because 27.8% of interferon-alpha-2b was retained after 24 h. These liposomes have the potential to be topically injected for treating genital herpes with prolonged interferon levels at the local injection site. Since the smaller liposomes (75.8 and 101 nm) retained interferon-alpha-2b at the injection site for shorter times while enhancing the blood circulation of the drug, they are potentially good carriers for systemic therapy with higher bioavailability and liver targeting.