This invention relates to pharmaceutical formulations and formulation strategies of protides (phosphoramidate derivatives of nucleosides) and, in particular, protides useful in the treatment of cancer such as NUC-3373 (5-fluoro-2'-deoxyuridine-5'-0-[1-naphthyl (benzoxy-L-alaninyl)] phosphate) and NUC-7738 (3'-deoxyadenosine-5'-0-[phenyl(benzyloxy-L-alaninyl)] phosphate). In particular, the invention relates to formulations which comprise a polar aprotic solvent, for example dimethyl acetamide (DMA).