Formulation and characterisation of primaquine loaded liposomes prepared by a pH gradient using experimental design

The effect of different formulation factors (lipid type, cholesterol, charg e, internal buffer capacity, drug-to-lipid incubation ratio On the encapsul ation efficiency and size of primaquine liposomes (SUV's) in response to a pH gradient was investigated by a fractional factorial screening design. Th ree of the factors (charge, internal buffer capacity, drug-to-lipid incubat ion ratio) were further studied in a Box-Behnken optimisation design. The l ipid type was the most important parameter followed by the drug-to-lipid in cubation ratio, buffer capacity, cholesterol and charge. Several of the int eractions were important. In the optimisation design a robust region with h igh encapsulation efficiency (> 95%) was obtained for DSPC: 33.33 mol% chol esterol-liposomes at high internal citrate concentration (200 nM) by mainta ining the drug-to-lipid incubation ratio below 0.15:1 (mol:mol) and varying the charge incorporation between 2 and 10%. In order to achieve long-term stability and sterility, the liposomes were lyophilised followed by gamma i rradiation, The pH gradient was maintained during this treatment with littl e chemical degradation of the substances. The final preparation consisted o f three separate vials with lyophilised liposomes, solid state primaquine a nd hydration medium, (C) 2000 Elsevier Science B.V. All rights reserved.