Compositions and methods for modifying biologically active substances to achieve multi-day delivery of such substances, particularly through oral or parenteral administration, are disclosed. The compositions include the biologically active substance conjugated to a carrier having a suitably long half life, typically more than one day, wherein the conjugate optionally contains a spacer linking the carrier to the biologically active substance. Pharmaceutical formulations of the conjugates are also disclosed, as are methods of extending delivery of a single dose of a biologically active substance for more than one day.
