Factors affecting the size distribution of liposomes produced by freeze-thaw extrusion

Int J Pharm. 1999 Oct 15;188(1):87-95. doi: 10.1016/s0378-5173(99)00207-0.


This paper describes the development of a protocol for the production of liposomes using a freeze-thaw extrusion methodology. Laser diffraction particle size analysis showed that the median diameter of freeze-thawed egg phosphatidylcholine multilamellar vesicles (eggPC MLVs) was increased when cholesterol was included in the bilayers. Using a freeze-thaw cycle of 3 min freezing in liquid nitrogen at -196 degrees C followed by 3 min thawing at 50 degrees C resulted in an anomalously large particle size for eggPC/cholesterol formulations. When liposomes were repeatedly freeze-thawed a maximum size was achieved after five freeze-thaw cycles. Dispersion of liposomes in sodium chloride solutions promoted size increases following freeze-thawing, suggesting that vesicles had aggregated or fused. Poloxamers P338 and P407 inhibited the size increases observed during freeze-thawing for eggPC MLVs dispersed in 1.0 M NaCl, probably through steric prevention of aggregation and fusion.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Chemistry, Pharmaceutical / methods
  • Cholesterol / chemistry
  • Dose-Response Relationship, Drug
  • Drug Stability
  • Freeze Drying
  • Freezing*
  • Hot Temperature
  • Liposomes / chemistry*
  • Liposomes / drug effects
  • Particle Size
  • Phosphatidylcholines / chemistry
  • Poloxamer / pharmacology
  • Sodium Chloride / pharmacology
  • Solutions


  • Liposomes
  • Phosphatidylcholines
  • Solutions
  • Poloxamer
  • Sodium Chloride
  • Cholesterol