Trimethoprim (TMP) is an antibiotic that is mainly used to treat bladder infections. Other uses include middle ear infections and traveler's diarrhea. In combination with sulfamethoxazole or dapsone, it can be used for pneumocystis pneumonia in people with HIV/AIDS. It is taken by mouth. Trimethoprim is on the WHO essential medicines list and requires a prescription.



Trimethoprim binds to dihydrofolate reductase and inhibits the reduction of dihydrofolic acid (DHF) to tetrahydrofolic acid (THF). THF is an essential building block for DNA synthesis. The affinity of trimethoprim for bacterial dihydrofolate reductase is several thousand times greater than its affinity for human dihydrofolate reductase. Thus, the effects on human DNA synthesis are comparatively small.


Maximum plasma concentration is usually reached at 1-4 hours after ingestion. Approximately 44% of the drug is present bound to plasma proteins. The metabolism of trimethoprim is mainly catalyzed by the enzymes CYP2C9 and CYP3A4. Excretion is largely via the urine.


Side effects

Common side effects:

  • Nausea
  • Taste changes
  • Vomiting
  • Diarrhea
  • Rash
  • UV sensitivity
  • Itch

Rare side effects

  • thrombocytopenia (low platelet count)
  • megaloblastic anemia
  • increased potassium levels (hyperkalemia)
  • increase in serum creatinine
  • use in EHEC infections may lead to increased expression of Shiga toxin

Toxicological data

LD50 (mouse, oral) 2764 mg-kg-1

Chemical & physical properties

ATC Code J01EA01
Formula C14H18N4O3
Molar Mass (g·mol−1) 290,32
Physical State solid
Melting Point (°C) 199–203
PKS Value 7,12
CAS Number 738-70-5
PUB Number 5578
Drugbank ID DB00440


  • Drugbank
  • PubChem
  • Aktories, Förstermann, Hofmann, Starke: Allgemeine und spezielle Pharmakologie und Toxikologie, Elsvier, 2017

Editorial principles

All information used for the content comes from verified sources (recognised institutions, experts, studies by renowned universities). We attach great importance to the qualification of the authors and the scientific background of the information. Thus, we ensure that our research is based on scientific findings.
Markus Falkenstätter, BSc

Markus Falkenstätter, BSc

Markus Falkenstätter is a writer on pharmaceutical topics in Medikamio's medical editorial team. He is in the last semester of his pharmacy studies at the University of Vienna and loves scientific work in the field of natural sciences.

Mag. pharm. Stefanie Lehenauer

Mag. pharm. Stefanie Lehenauer

Stefanie Lehenauer has been a freelance writer for Medikamio since 2020 and studied pharmacy at the University of Vienna. She works as a pharmacist in Vienna and her passion is herbal medicines and their effects.

The content of this page is an automated and high-quality translation from DeepL. You can find the original content in German here.


Your personal medicine assistent

afgis-Qualitätslogo mit Ablauf Jahr/Monat: Mit einem Klick auf das Logo öffnet sich ein neues Bildschirmfenster mit Informationen über medikamio GmbH & Co KG und sein/ihr Internet-Angebot: This website is certified by Health On the Net Foundation. Click to verify.

Search our database for drugs, sorted from A-Z with their effects and ingredients.


All substances with their common uses, chemical components and medical products which contain them.


Causes, symptoms and treatment for the most common diseases and injuries.

The contents shown do not replace the original package insert of the medicinal product, especially with regard to dosage and effect of the individual products. We cannot assume any liability for the correctness of the data, as the data was partly converted automatically. A doctor should always be consulted for diagnoses and other health questions. Further information on this topic can be found here.