5-Chloro-O-demethyl-3-decyano Ricinine-d3 is deuterium labelled form of 5-Chloro-O-demethyl-3-decyano Ricinine (C370845), which is the impurity of antitumor agent Gimeracil (G378000) that is a potent inhibitor of dihydropyrimidine dehydrogenase (DPD).