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]
For the treatment of urinary tract infections, uncomplicated pyelonephritis (with sulfamethoxazole) and mild acute prostatitis. May be used as pericoital (with sulfamethoxazole) or continuous prophylaxis in females with recurrent cystitis. May be used as an alternative to treat asymptomatic bacteriuria during pregnancy (only before the last 6 weeks of pregnancy). Other uses include: alternative agent in respiratory tract infections (otitis, sinusitus, bronchitis and pneumonia), treatment of Pneumocystis jirovecii pneumonia (acute or prophylaxis), Nocardia infections, and traveller's diarrhea.
Trimethoprim is a pyrimidine analogue that disrupts folate synthesis, an essential part of the thymidine synthesis pathway. Inhibition of the enzyme starves the bacteria of nucleotides necessary for DNA replication.The drug, therefore, exhibits bactericidal activity.
Mechanism of action
Trimethoprim binds to dihydrofolate reductase and inhibits the reduction of dihydrofolic acid (DHF) to tetrahydrofolic acid (THF). THF is an essential precursor in the thymidine synthesis pathway and interference with this pathway inhibits bacterial DNA synthesis. Trimethoprim's affinity for bacterial dihydrofolate reductase is several thousand times greater than its affinity for human dihydrofolate reductase. Sulfamethoxazole inhibits dihydrofolate synthetase (aka dihydropteroate synthetase), an enzyme involved further upstream in the same pathway. Trimethoprim and sulfamethoxazole are commonly used in combination due to their synergistic effects. This drug combination also reduces the development of resistance that is seen when either drug is used alone.
Route of administration
Anti-Infective Agents, Urinary
Antibacterials for Systemic Use
Antiinfectives for Systemic Use
Chemical Actions and Uses
Cytochrome P-450 CYP2C8 Inhibitors
Cytochrome P-450 CYP2C8 Inhibitors (moderate)
Cytochrome P-450 CYP2C8 Substrates
Cytochrome P-450 CYP2C9 Inhibitors
Cytochrome P-450 CYP2C9 Inhibitors (moderate)
Cytochrome P-450 CYP2C9 Substrates
Cytochrome P-450 CYP3A4 Substrates
Cytochrome P-450 Enzyme Inhibitors
Drug-Related Side Effects and Adverse Reactions
Folic Acid Antagonists
Heterocyclic Compounds, 1-Ring
Metabolic Side Effects of Drugs and Substances
Molecular Mechanisms of Pharmacological Action
QTc-Prolonging Agents (Indeterminate Risk and Risk Modifying)
Drug Info/Drug Targets: DrugBank 3.0: a comprehensive resource for 'omics' research on drugs. Knox C, Law V, Jewison
T, Liu P, Ly S, Frolkis A, Pon A, Banco K, Mak C, Neveu V, Djoumbou Y, Eisner R, Guo AC, Wishart DS.
Nucleic Acids Res. 2011 Jan; 39 (Database issue):D1035-41. | PMID:21059682