<prompt> Which of the following is dihydroorotate dehydrogenase inhibitor?MethotrexateLeflunomideHydroxychloroquineSulfasalazine  <response>: Ans. is b i.e., Leflunomide Important DMARDsMechanism of action MethotrexateDihydrofolate reductase inhibitor SulfasalazineSulfapyridine moiety suppresses the generation of superoxide radicals and cytokine production LeflunomideIs rapidly converted in the body to an active metabolite which inhibits dihydroorotate dehydrogenase. Hydroxychloroquine Reduce monocyte IL-1, consequently inhibiting B-cells Interferes with antigen processing Stabilizes lysosome and free radical scavenging. 