Mycophenolic acid is an immunosuppressant drug most commonly used to prevent organ rejection after transplant. This drug has frequently replaced steroids in the treatment of immune-mediated disorders. Mycophenolate, derived from Penicillin stoloniferum, is metabolized in the liver to the active metabolite mycophenolic acid. This metabolite inhibits iosine monophosphate dehydrogenase, the enzyme that controls the rate of synthesis of guanine monophosphate in the de novo pathway of purine synthesis used in the proliferation of B and T lymphocytes.