Also known as fumaric acid esters under the brand name Efudex, this is a chemotherapy drug. When applied topically, it is considered one of the primary options for the treatment of psoriasis affecting the nails. It can also be taken orally for severe psoriatic symptoms. (Sources: Clinical Dermatology, September-October 2008, pages 522-526; British Journal of Dermatology, September 2005, pages 549-551, and April 2004, pages 741-746; and Cutis, July 1998, pages 27-28.)