UTI Knowledge Center
Antibiotic Spotlight

Trimethoprim

Emery Haley, PhD, Scientific Writing Specialist

Trimethoprim

Find the Latest FDA-Approved Labelling Information Here: Drugs@FDA Online Database

Administrative Routes

Oral (PO)

Other Names

Primsol; TMP

Bacteriostatic or Bactericidal

Bacteriostatic [1]

Antibiotic Class

Trimethoprim

Mechanisms of Action

Trimethoprim is a direct competitor of the bacterial dihydrofolate reductase enzyme. Inhibition prevents the conversion of dihydrofolic acid to tetrahydrofolic acid, the active form of folate. Lack of active folate prevents bacterial DNA, RNA, and protein synthesis, necessary for bacterial growth.

WHO AWaRe Classification

Access [2]

Empiric Use Recommendations

Yes (lower UTI/cystitis) [World Health Organization (WHO)] [3]

Indication(s) Relevant to UTI

On label for uncomplicated UTIs caused by Escherichia coli, Proteus mirabilis, Klebsiella pneumoniae, Enterobacter species, or Coagulase-negative Staphylococci (including Staphylococcus saprophyticus).

Checkmarks

CLSI and/or FDA documents support the efficacy of this antibiotic against the following organisms from the Guidance® UTI test: Citrobacter freundii, Citrobacter koseri, Coagulase-negative Staphylococci, Escherichia coli, Enterobacter Group organisms, Klebsiella oxytoca, Klebsiella pneumoniae, Morganella morganii, Proteus mirabilis, Providencia stuartii, Staphylococcus aureus, and Serratia marcescens.

About the Author

Dr. Emery Haley is a scientific writing specialist with over ten years of experience in translational cell and molecular biology. As both a former laboratory scientist and an experienced science communicator, Dr. Haley is passionate about making complex research clear, approachable, and relevant. Their work has been published in over 10 papers and focuses on bridging the gap between the lab and real-world patient care to help drive better health outcomes.

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References
  1. Ishak, A.; Mazonakis, N.; Spernovasilis, N.; Akinosoglou, K.; Tsioutis, C. Bactericidal versus Bacteriostatic Antibacterials: Clinical Significance, Differences and Synergistic Potential in Clinical Practice. J. Antimicrob. Chemother. 2024, 80, 1–17, doi:10.1093/jac/dkae380
  2. AWaRe Classification of Antibiotics for Evaluation and Monitoring of Use, 2023 Available online: https://www.who.int/publications/i/item/WHO-MHP-HPS-EML-2023.04 (accessed on 6 February 2025).
  3. The WHO AWaRe (Access, Watch, Reserve) Antibiotic Book – Infographics – PAHO/WHO | Pan American Health Organization Available online: https://www.paho.org/en/documents/who-aware-access-watch-reserve-antibiotic-book-infographics (accessed on 22 July 2025).