🦠microbiology review

Trimethoprim

Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025

Definition

Trimethoprim is an antibiotic used primarily to treat bacterial infections, particularly in the urogenital and digestive systems. It works by inhibiting bacterial DNA synthesis.

5 Must Know Facts For Your Next Test

  1. Trimethoprim specifically inhibits the bacterial enzyme dihydrofolate reductase.
  2. It is often combined with sulfamethoxazole to enhance its antibacterial efficacy, forming the drug known as co-trimoxazole.
  3. Trimethoprim is effective against a broad spectrum of Gram-positive and Gram-negative bacteria.
  4. It is commonly used to treat urinary tract infections (UTIs) and traveler's diarrhea.
  5. Bacterial resistance to trimethoprim can occur via mutations in the target enzyme dihydrofolate reductase.

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