The sodium salt form of mycophenolic acid (MPA), with immunosuppressing activity. In vivo, the active molecule MPA reversibly inhibits inosine monophosphate dehydrogenase (IMPDH) which is needed for guanine monophosphate synthesis and stops the proliferation of B and T lymphocytes. Relative to other cell types, lypmocytes are highly dependent on salvage and de novo synthesis of guanine nucleotides, thus making these cells prone to MPA cytotoxicity.