This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunomodulator, Subject name: Pharmacology
Which of the following is dihydroorotate dehydrogenase inhibitor? 
Select and explain. 
A. Methotrexate, B. Leflunomide, C. Hydroxychloroquine, D. Sulfasalazine
B: Leflunomide
Answer: B: Leflunomide 
Explanation: 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.