Mycophenolic acid is a small lactone antibiotic produced by Pen. brevicom pactum and Pen. stoloniferum. Activity against gram-positive bacteria. In animal experiments, it has inhibitory effect on sarcoma-180, Lewis lung cancer, adenocarcinoma Ca-755, Walker tumor 256, Yoshida sarcoma, Freund ascites tumor, etc. Mycophenolic acid is a potent IMPDH inhibitor and the active metabolite of an immunosuppressive drug, used to prevent rejection in organ transplantation. It inhibits an enzyme needed for the growth of T cells and B cells.