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Liposomes based on aqueous encapsulation of drugs exhibit known physical and chemical instability, which both limit their widespread use and often lead to shortened product shelf life. Recognized formulation degradation issues for this class of drugs during long-term storage include phospholipid oxidation, liposome aggregation or fusion, lack of redispersibility, and drug leakage. These defects have resulted in greater quality risks and control costs for liposome products, and many well-known liposome drug safety incidents have occurred.

Lyophilization, also known as freeze-drying, is considered a major strategy to reduce the known stability risks of liposomal formulations and improve the shelf-life of liposome-based drugs. Lyophilized clodronate liposomes are products obtained from clodronate liposomes through a special freeze-drying process. The lyophilized product only needs to be reconstituted by adding sterile pure water and mixed to obtain the standard solution.

Production Process

A typical freeze-drying process consists of three main stages:

  • Freezing

During the freezing stage, the temperature is lowered and most of the solvent is separated from the liposomes and excipients, thereby forming ice crystals. Due to the increase in ice crystal size, annealing of frozen samples can also be introduced to reduce sample heterogeneity and reduce drying rates.

  • Primary drying

When the pressure drops to a few millibars, the temperature on the shelf rises to provide the heat required for sublimation to begin primary drying.

  • Secondary drying

During secondary drying, the temperature is further increased to allow desorption of water.

All of these steps may be critical to the integrity of the liposomes and retention of entrapped compounds. In addition, in these steps, many other factors will affect the quality of the final product, and the liposome lyophilization process for different products is different.

Schematic representation of the  factors influencing the critical quality attributes of freeze-dried liposomesFig. 1 Schematic representation of the factors influencing the critical quality attributes of freeze-dried liposomes (Franzé S, 2018)


  • Dry stability, including reduced solid-state aggregation and degradation of the drug (e.g., hydrolysis), ready solid redispersibility (no clumping, agglomeration, or insolubility) upon reconstitution in aqueous solutions, and solid lyophilization for injection
  • Storage stability in the dry state
  • The reconstitution of the lipid bilayer after adding water before administration without drug leakage
  • The reconstituted solution of the lyophilized powder not only has a better shape and shorter reconstitution time, but also is indistinguishable from standard liposome solution

Quality Control

The basic dosage form evaluation criteria for lyophilized powder include

  • Liposome formulation
  • Particle size distribution
  • Surface Zeta potential
  • Drug encapsulation
  • The residual moisture content

Reconstitution of Lyophilized Clodronate Liposomes

Sterile water is recommended for reconstitution. Add 4.7 ml sterile pure water into the vial at room temperature and mix by inverting the vial several times. Let it stand on the bench for 2-3 min and vortex 2-3 times (20-30 sec each time) at medium speed. The liposomes can be used within 10 min after reconstitution. Make sure there are no lumps or noticeable particles. Vortex more if this occurs until homogeneous. Sterilely reconstituted products can be stored in the refrigerator for up to 3 months when handled cleanly.


  1. Franzé S; et al. Lyophilization of Liposomal Formulations: Still Necessary, Still Challenging. Pharmaceutics. 2018 Aug 28; 10(3): 139.
  2. Misra A; et al. Recent advances in liposomal dry powder formulations: preparation and evaluation. Expert Opin Drug Deliv. 2009 Jan; 6(1): 71-89.

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