| Item |
Information |
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Drug Groups
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approved |
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Description
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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] |
| Indication |
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. |
| Pharmacology |
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. |
| Toxicity |
LD50=4850 (orally in mice) |
| Affected Organisms |
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Gram negative and gram positive bacteria |
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| Biotransformation |
Hepatic metabolism to oxide and hydroxylated metabolites. |
| Absorption |
Readily and almost completely absorbed in the GI tract with peak serum concentrations attained 1-4 hours after oral administration. Widely distributed to tissues and fluids including kidney, lung, seminal fluid, aqueous humour, middle ear fluid, sputum, vaginal secretions, bile, bone and CSF. |
| Half Life |
8-11 hours in adults with normal renal function |
| Protein Binding |
42-46% bound to plasma proteins |
| Elimination |
Ten to twenty percent of trimethoprim is metabolized, primarily in the liver; the remainder is excreted unchanged in the urine.
After oral administration, 50% to 60% of trimethoprim is excreted in the urine within 24 hours, approximately 80% of this being unmetabolized trimethoprim. Trimethoprim also passes the placental barrier and is excreted in human milk. |
| References |
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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]
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Brumfitt W, Hamilton-Miller JM: Limitations of and indications for the use of co-trimoxazole. J Chemother. 1994 Feb;6(1):3-11.
[Pubmed]
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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]
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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]
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Johnson JR, Manges AR, O'Bryan 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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