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Trimethioprim: Full Drug Profile

Medically reviewed by Min Clinic Staff | Updated: January 2026

Trimethioprim - General Information

A pyrimidine inhibitor of dihydrofolate reductase, it is an antibacterial related to pyrimethamine. The interference with folic acid metabolism may cause a depression of hematopoiesis. It is potentiated by sulfonamides and the trimethoprim-sulfamethoxazole combination is the form most often used. It is sometimes used alone as an antimalarial. trimethoprim resistance has been reported. [PubChem]

 

Pharmacology of Trimethioprim

Trimethioprim, a synthetic antiinfective agent, is used to treat and prevent urinary tract infections, diarrhea, and, when combined with either sulfamethoxazole or dapsone, Pneumocystis carinii infections.

 

Trimethioprim for patients

 

Trimethioprim Interactions

Trimethoprim may inhibit the hepatic metabolism of phenytoin. Trimethoprim, given at a common clinical dosage, increased the phenytoin half-life by 51% and decreased the phenytoin metabolic clearance rate by 30%. When administering these drugs concurrently, one should be alert for possible excessive phenytoin effect.

 

Trimethioprim Contraindications

Trimethoprim is contraindicated in individuals hypersensitive to trimethoprim and in those with documented megaloblastic anemia due to folate deficiency.

 

Additional information about Trimethioprim

Trimethioprim Indication

For the treatment of initial episodes of uncomplicated urinary tract infections

Mechanism Of Action
Trimethioprim binds to bacterial dihydrofolate reductase, subsequently interfering with the uptake of p-aminobenzoic acid (PABA) into folic acid. As folic acid is a coenzyme responsible for the transport of one-carbon fragments from one molecule to another, it is an essential component of bacterial development. Sulfonamides inhibit bacterial dihydrofolate synthetase, the enzyme immediately preceding dihydrofolate reductase, and therefore act synergistically with trimethoprim.
Food Interactions
Take on empty stomach: 1 hour before or 2 hours after meals.
Generic Name
Trimethoprim
Drug Category
Antimalarials; Anti-Infectives
Drug Type
Small Molecule; Approved
Other Brand Names containing Trimethoprim
Abacin; Abaprim; Alprim; Apo-Sulfatrim; Bactin; Bactramin; Bactrim; Bactrim DS; Bactrim Pediatric; Baktar; Chemotrim; Co-Trimoxazole; Comox; Cotrim; Cotrim D.S.; Drylin; Eusaprim; Fectrim; Gantaprim; Gantrim; Idotrim; Imexim; Instalac; Ipral; Kepinol; Laratrim; Lidaprim; Linaris; Methoprim; Microtrim; Monoprim; Monotrim; Monotrimin; Nopil; Oraprim; Priloprim; Primosept; Primsol; Proloprim; Septra; Septra DS; Septra Grape; Septrin; Sigaprim; Sulfamethoprim; Sulfamethoprim-DS; Sulfamethoxazole & Trimethoprim; Sulfatrim; Sulfatrim Pediatric; Sulfatrim-DS; Sulfatrim-SS; Sulfotrim; Sulmeprim; Sulmeprim Pediatric; Sulprim; Sumetrolim; Supracombin; Suprim; Syraprim; Teleprim; Thiocuran; Tiempe; Tmp-Ratiopharm; Trigonyl; Trimanyl; Trimesulf; Trimeth/Sulfa; Trimethioprim; Trimethopriom; Trimetoprim; Trimexazole; Trimogal; Trimopan; Trimpex; Trimpex 200; Triprim; Unitrim; Uretrim; Uro-Septra; Uroplus; Uroplus DS; Uroplus SS; Wellcoprim;
Toxicity (Overdose)
LD50=4850 (orally in mice)
Protein Binding
Approximately 45%
Half Life
8-10 hours
Dosage Forms of Trimethioprim
Tablet Oral
Chemical IUPAC Name
5-[(3,4,5-trimethoxyphenyl)methyl]pyrimidine-2,4-diamine
Chemical Formula
C14H18N4O3
Organisms Affected
Gram negative and gram positive bacteria