Sulfonamides · Pharmacology

Which enzyme is targeted by Trimethoprim, the agent frequently combined with Sulfamethoxazole?

  1. Dihydropteroate synthase
  2. Dihydrofolate reductase
  3. Thymidylate synthase
  4. RNA polymerase
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Correct answer: Dihydrofolate reductase

Trimethoprim inhibits dihydrofolate reductase, which is the step following the sulfonamide target in the folic acid synthesis pathway. The combination of the two drugs results in sequential blockade and synergistic bactericidal activity.

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