Figure 5. Maximum capture of gefitinib in remote-loaded liposomes.

The efficiency, maximum capacity, and reproducibility of gefitinib encapsulation in DSPC:PEG-DSPE:Chol (9:1:5 mol:mol:mol) liposomes by remote loading was evaluated for 4 sets of formulations differing in initial drug:lipid ratio (0.20–1.30 mol:mol) that were prepared over a period of 5 mos. Ammonium sulfate was the intra-luminal trapping ion. After loading, free drug was removed by dialysis and brief centrifugation (6 min, 7500g) to ensure formulations were free of precipitated drug. Gefitinib was quantified based on absorbance values at 345 nm by comparison to a standard curve after dissolution of the liposomes in 1:1 (v/v) chloroform:methanol. Phospholipid concentrations were determined by inorganic phosphate assay after digestion in sulfuric acid ²⁰. Symbols represent the final drug:lipid ratio achieved (ordinate) at different initial drug:lipid loading ratios (abscissa). The solid line shows fitting of the data using a Hill function (WinNonlin^®, Pharsight Inc., St. Louis, MO). The curve fitting indicated that the liposome capacity for drug asymptotically approached a maximum of 57 mol% (drug:lipid), with a standard error of 9%.