Which class interferes with folic acid synthesis?

Which class interferes with folic acid synthesis?

• A. Sulfonamides
• B. Quinolones
• C. Macrolides
• D. Carbapenems

Answer: (A)

Interfering with folic acid synthesis is a hallmark of sulfonamides. These drugs act as competitive inhibitors by mimicking the bacterial substrate PABA in the folate synthesis pathway. By blocking dihydropteroate synthase, they prevent the production of dihydrofolic acid and downstream folate cofactors needed for making thymidine and purines. Without adequate folate, bacteria can’t effectively synthesize DNA, leading to inhibited growth. Humans don’t synthesize folate de novo and obtain it from the diet, so sulfonamides achieve selective toxicity for bacteria. Other antibiotic classes target different essential processes. Quinolones disrupt DNA replication by inhibiting DNA gyrase and topoisomerase IV. Macrolides bind the 50S ribosomal subunit, blocking protein synthesis. Carbapenems inhibit cell wall synthesis by targeting penicillin-binding proteins. None of these directly block folate synthesis, which is why the correct choice is the sulfonamides.

Interfering with folic acid synthesis is a hallmark of sulfonamides. These drugs act as competitive inhibitors by mimicking the bacterial substrate PABA in the folate synthesis pathway. By blocking dihydropteroate synthase, they prevent the production of dihydrofolic acid and downstream folate cofactors needed for making thymidine and purines. Without adequate folate, bacteria can’t effectively synthesize DNA, leading to inhibited growth. Humans don’t synthesize folate de novo and obtain it from the diet, so sulfonamides achieve selective toxicity for bacteria.

Other antibiotic classes target different essential processes. Quinolones disrupt DNA replication by inhibiting DNA gyrase and topoisomerase IV. Macrolides bind the 50S ribosomal subunit, blocking protein synthesis. Carbapenems inhibit cell wall synthesis by targeting penicillin-binding proteins. None of these directly block folate synthesis, which is why the correct choice is the sulfonamides.