Appeal No. 2006-2213 Page 2
Application No. 09/771,151
phase at a sufficiently high drug-to-lipid ratio for efficacious therapy remains a
problematic issue.” Page 2. The specification discloses that one may obtain a
liposome having an increased drug to lipid ratio by entrapping a supersaturated solution
of a drug within the liposome. Page 3.
To prepare a supersaturated solution of a drug compound, one must first select a
compound whose solubility can be increased at least two-fold over its room temperature
solubility. Page 6. The compound’s solubility can be increased by, e.g., raising the
temperature of the solvent, adding a co-solvent, or changing the pH of the solvent. Id.
The specification discloses that the anticancer drug cisplatin is suitable for use in
preparing supersaturated solutions because it is much more soluble at elevated
temperatures than at room temperature. Id. Thus, for example, a supersaturated
solution of cisplatin can be obtained by heating a solution containing cisplatin at a
concentration greater than its room temperature solubility limit. Pages 6-7.
To entrap the supersaturated solution within liposomes, a separately prepared
lipid composition is hydrated with the supersaturated solution of the drug. Page 7. The
specification discloses that the lipid preparation may contain lipids which are derivatized
with polymers such as polyethylene glycol. Id.
The resulting liposomes containing entrapped supersaturated solutions of drug
compounds can be prepared in desired sizes by known methods including sonication,
homogenization or extrusion. Page 8. The specification discloses that by adjusting the
size of the liposomes appropriately, one can inhibit precipitation of the drug from the
entrapped supersaturated solution, even under conditions in which the drug would
normally precipitate. Id.
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