This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: AIIMS 2018, Subject name: Pharmacology
Dapsone is used for treatment of bacterial and fungal infections as well as for immunomodulatory actions. What is mechanism of dapsone for these indication? 
Select and explain. 
A. Inhibition of cell wall synthesis, B. Inhibition of ergosterol in cell membranes, C. Inhibition of protein synthesis, D. Competition with PABA in folic acid synthesis
D: Competition with PABA in folic acid synthesis
Answer: D: Competition with PABA in folic acid synthesis 
Explanation: Sulfonamides (including Dapsone and PAS) : Competitively inhibit folic acid synthase enzyme as these are PABA analogues. Trimethoprim, Pyrimethamine : Inhibit Dihydro folate reductase enzyme (DHFRase). Inhibition of ergosterol in cell membrane (in fungus and leishmania): Amphotericin B.