Basics

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.

Pharmacology

Pharmacodynamics

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.

Pharmacokinetics

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.

Toxicity

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

Author

Markus Falkenstätter, BSc

Pharmacy student

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.

Reviewer

Mag. pharm. Stefanie Brandauer

Pharmacist

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.

Editorial principles

All information used for our content comes from verified sources (recognised institutions, specialists, studies by renowned universities). We place great value on the qualification of the authors and the scientific background of the information, so that our research is based on scientific evidence.