Azaribine (2′, 3′, 5′-triacetyl-6-azauridine) is the orally absorbable triacetylated derivative of the pyrimidine analog 6-azauridine. Ribonucleoside of 6-azauracil, which can be derived in the tissues by the deacetylation of azaribine, has been shown, after its intracellular conversion to 6-azauridine-5'-monophosphate, to serve as an inhibitor of the activity of a key enzyme, orotidine-5'-monophosphate (OMP) decarboxylase, critically concerned with the biosynthesis de novo of pyrimidines essential for the formation of nucleic acids. Azaribine exerts antineoplastic action. In 1975 azaribine was approved for the treatment of psoriasis. The drug was withdrawn because it may cause life-threatening or fatal blood clots in the veins and arteries.