Liposome Disposition in Vivo: Effects of Pre-dosing with Lipsomes

The effect of a high, intravenous dose of extruded multilamellar liposomes (1.1 g lipid/kg body weight) upon the subsequent ability of mouse tissues to take-up or bind a second intravenous dose of similar liposomes encapsulating 14C-inulin has been studied in vivo. The first and second doses were separated by either 1,5 or 24 hours. All tissue levels were measured one hour after the second dose. Controls received only the second dose. When the two doses were separated by one hours, 14C-levels in liver were depressed 6-fold and blood levels rose 29-fold relative to controls. However spleen uptake of lipsomes increased to three times control levels. When the two doses were separated by 24 hrs, the first dose had only a minimal effect on the disposition of the second dose. The results are consistent with a reversible blockade of hepatic, but not spleenic uptake and/or binding sites, by the first dose and indicate that adjusting a liposome dose (i.e. number of lipsomes) or use of a drug-free liposome pre-dose may be a useful technique for reducing hepatic uptake, increasing the circulation life time and/or modifying the tissue disposition properteries of therapeutic liposomes without changing liposome composition or size.