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.
Mode 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.
Hepatic metabolism to oxide and hydroxylated metabolites.
LD50=4850 (orally in mice)
Brumfitt W, Hamilton-Miller JM: Reassessment of the rationale for the combinations of sulphonamides with diaminopyrimidines. J Chemother. 1993 Dec;5(6):465-9. Pubmed Brumfitt W, Hamilton-Miller JM: Limitations of and indications for the use of co-trimoxazole. J Chemother. 1994 Feb;6(1):3-11. Pubmed Bean DC, Livermore DM, Papa I, Hall LM: Resistance among Escherichia coli to sulphonamides and other antimicrobials now little used in man. J Antimicrob Chemother. 2005 Nov;56(5):962-4. Epub 2005 Sep 8. Pubmed Felmingham D, Reinert RR, Hirakata Y, Rodloff A: Increasing prevalence of antimicrobial resistance among isolates of Streptococcus pneumoniae from the PROTEKT surveillance study, and compatative in vitro activity of the ketolide, telithromycin. J Antimicrob Chemother. 2002 Sep;50 Suppl S1:25-37. Pubmed Johnson JR, Manges AR, OêBryan TT, Riley LW: A disseminated multidrug-resistant clonal group of uropathogenic Escherichia coli in pyelonephritis. Lancet. 2002 Jun 29;359(9325):2249-51. Pubmed
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