The Preparation of Large Volumes of Homogeneous, Sterile Liposomes Containing Various Lipophilic Cytostatic Drugs by the Use of a Capillary Dialyzer

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Abstract
A dialysis method for the preparation of large volumes of stable and homogeneous bilayer liposomes under sterile conditions was developed. The equipment consists of a disposable hemodialysis capillary dialyzer connected to two reservoirs through which the micelle/liposome solution is pumped in a closed circuit. The detergent is removed by a countercurrent flow of the dialysis buffer. Homogeneous, detergent fjree liposome preparations totaling 100 ml with lipid concentrations ranging from 5 to 25 mg/ml can be prepared within 2-4 hours. Greater lipid concentrations or larger batch volumes can be obtained with dialyzing cartridges allowing for higher detergent clearing performances. The incorporation of lipophilic derivatives of the cytostatic drugs 1β-D-arabinofuranosyl cytosine (ara-C) and 5′-fluoro-2′-deoxy uridine (FUdR) is nearly quantitative, and stable, homogeneous bilayer liposomes of about 100 nanometers in diameter are obtained. Liposomes with prodrug concentrations of 2 to 10 mg per milliliter can be prepared depending upon the lipid amounts used. Free ara-C or generally small and water soluble molecules however, cannot be encapsulated within the liposomes due to quantitative loss during dialysis.