Immunopotentiators can be adsorbed to insoluble metal salts, such as aluminium salts, to modify their pharmacokinetics, pharmacodynamics, intramuscular retention time, and/or immunostimulatory effect. Immunopotentiators are modified to introduce a moiety, such as a phosphonate group, which can mediate adsorption. These modified compounds can retain or improve their in vivo immunological activity even when delivered in an adsorbed form.