158 Scientific Basis of Healthcare: Arthritis 8 Drugs in Focus in Arthritis: Leflunomide Stefano Alivernini, 1,a, * Elisa Gremese 1,b and Gianfranco Ferraccioli 1,c ABSTRACT Leflunomide is an inhibitor of dihydro-orotate dehydrogenase (DHODH), a mytochondrial enzyme important for de novo synthesis of pyrimidine ribonucleotides. It blocks the proliferation of human T lymphocytes thus leading to the arrest in the G 1 /S phase of the cell cycle and to the interruption of T lymphocytes clonal expansion. Leflunomide has been shown to inhibit the activation of NF-kB being able to block TNF-mediated NF-kB activation in a dose- and time dependent manner. Clinical trials have shown similar efficacy to methotrexate. The side effects are mainly at the gastrointestinal, lung and liver level. Efficacy and tolerability have been shown to be similar in adult and elderly patients. 1 Division of Rheumatology, School of Medicine, Catholic University of the Sacred Heart, Italy. a Email: stefano.alivernini@hotmail.it b Email: elisa.gremese@rm.unicatt.it c Email: gf.ferraccioli@rm.unicatt.it List of abbreviations after the text.