Poly(methacrylic acid)-induced liposome aggregation for measuring drug entrapment.

This report characterizes a procedure for rapidly and accurately determining the entrapment of vincristine or other water-soluble drugs in polyethylene glycol-derivatized liposomes. Rapid liposome aggregation with poly(methacrylic acid) and pelleting by mild centrifugation separates liposome-associated vincristine from unentrapped drug. After collecting the supernatant fraction, the pellet is resuspended and solubilized in isopropyl alcohol. Quantitative uv spectrophotometry determines vincristine mass in both fractions. The mean accuracy (recovery) is 100.6% over an entrapped drug range from 70 to 99%. Within and between day precision of the method has a relative standard deviation of 0.76% for a single measurement.