Thiopurine

The thiopurine drugs are purine antimetabolites widely used in the treatment of acute lymphoblastic leukemia, autoimmune disorders (e.g., Crohn's disease, rheumatoid arthritis), and organ transplant recipients.

Metabolism is catalyzed by S-methyltransferase.

Litigation over patents covering diagnostic kits to monitor the dosing of these drugs led to a US Supreme Court case, Mayo Collaborative Services v. Prometheus Laboratories, Inc. that dramatically changed the nature of patent law in the United States.