99mTechnetium-stannous oxinate as marker of liposome formulations

Liposomes associated with tin(II) dioxinate were prepared from egg yolk phosphatidylcholine and cholesterol as sterile and pyrogen-free multilamellar or unilamellar vesicles. Complexing of liposomal tin(II) dioxinate with 99mTc attained 98% of the added radioactivity. Thirty percent 99mTc were released during 24-h incubation in biological fluids. The absence of tin colloids seen by electron microscopy and the stability of liposomal phospholipid and tin(II) dioxinate during 72-h incubation at 37 degrees C in plasma and cerebrospinal fluid would allow safe and reliable scintigraphic liposome pharmacokinetic studies.