Allopurinol riboside is a metabolite of allopurinol, a xanthine oxidase inhibitor indicated for the management of patients with leukemia, lymphoma, and solid tumor malignancies who are receiving cancer therapy which causes elevations of serum and urinary uric acid levels and who cannot tolerate oral therapy. Allopurinol riboside is not an inhibitor of xanthine oxidase. Allopurinol riboside is commonly thought to be directly synthesized by purine nucleoside phosphorylase (PNP) in vivo. Allopurinol riboside competitively inhibits the action of PNP on inosine in vitro. Allopurinol riboside potently inhibits growth in vitro of promastigotes of Leishmania species. Patients with American cutaneous leishmaniasis who received allopurinol riboside had clinical improvement. In addition, allopurinol riboside demonstrated some effectivity against Trypanosoma cruzi infections in animals.