Provided herein are water-soluble prodrugs. The prodrugs of the invention comprise the water-soluble polymer PEG having four arms, which are covalently attached to an active agent, e.g. a small molecule. The conjugates of the invention provide an optimal balance of polymer size and structure for achieving improved drug loading, since the conjugates of the invention possess four active agents releasably attached to a four-armed water soluble polymer. The prodrugs of the invention are therapeutically effective, and exhibit improved properties in vivo when compared to unmodified parent drug.
