An antineoplastic antibiotic derived from various Penicillium fungal species. Mycophenolic acid is an active metabolite of the prodrug mycophenolate mofetil. Mycophenolic acid inhibits inosine monophosphate dehydrogenase (IMPDH), preventing the formation of guanosine monophosphate and synthesis of lymphocyte DNA that results in inhibition of lymphocyte proliferation, antibody production, cellular adhesion, and migration of T and B lymphocytes. Mycophenolic acid also has antibacterial, antifungal, and antiviral activities.