Modulation of drug loading in multivescular liposomes

Abstract

Disclosed is a method for making liposomes, for example multivesicular liposomes (MVLs), containing one or more biologically active agents, wherein the loading of the active agents into the liposomes is modulated by adjusting the osmolarity of the aqueous component into which the agents are dissolved prior to encapsulation. To increase the loading of the active agent, the osmolarity of the aqueous component is reduced, and to decrease the loading of the active agent, the osmolarity of the aqueous component is increased. In the making of MVLs, the process involves dissolving the active agent and an optional osmotic excipient in a first aqueous component encapsulated within the liposomes. For any given concentration of drug, the osmolarity of the first aqueous component can be adjusted by increasing or decreasing the concentration or molecular weight of the osmotic excipients used therein. The rate of release of the active agent into the surrounding environment in which the liposomes are introduced can be simultaneously controlled by incorporating into the lipid component used in the formulation at least one long chain amphipathic lipid. For example, the amphipathic lipid can have from about 13 to about 28 carbons in its carbon chain. Use of the long chain amphipathic lipid in the lipid component is particularly helpful in controlling the release rate and encapsulation efficiency for high drug load formulations.