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Repeated USMLE Questions Step 1- 172




A 22-year-old woman presents to the clinic for a recurrent urinary tract infection. She is prescribed trimethoprim/sulfamethoxazole.

What is the mechanism of action of this antimicrobial drug?

A- Inhibition of bacterial wall synthesis

B- Inhibition of folic acid synthesis

C- Inhibition of bacterial protein synthesis

D- Inhibition of mycolic acid synthesis

E- Inactivation of bacterial toxins

Answer




Sulfonamides act as antimicrobial agents through inhibition of folic acid synthesis, which leads to inhibition of bacterial nucleic acid synthesis. Penicillin and cephalosporin are involved in inhibition of bacterial cell wall synthesis. Inhibition of bacterial protein synthesis is the mechanism of action of aminoglycosides while inhibition of mycolic acid synthesis is the main action of isoniazid. Sulfonamides have no role in inactivation of bacterial toxins.

The correct answer is B







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