Effect of human plasma on the stability of large multilamellar liposomes with digitoxin

Abstract

The stability of multilamellar liposomes with digitoxin in human plasma at 37° C is studied “in vitro”. It is noted that as plasma/liposomal suspension ratio is increased, the porcentage of drug retained in the liposomes decreases. Just so, independently from the dosage form, the efflux rate is maximum during the first hour and then falls gradually and in a non linear way. The physical state of the bilayer is a conditioning factor in the release of the encapsulated drug. The dosage forms of egg yolk phosphatidylcholine (EYPC) and of dimiristoylphosphatidylcholine (DMPC) quickly release digitoxin; while dipalmitoylphosphatidylcholine (DPPC) retains 54% of the entrapped drug after 24 hours incubation with 80% of plasma at 37°C. The inclusion of cholesterol (CHOL) and dicetylphosphate (DCP) in the liposomal matrix neither aids in the incorporation of digitoxin to the liposomes, nor augments the stability of the system in the human plasma.