Trimethoprim

- Overview
  - Trimethoprim is a synthetic derivative of trimethoxybenzyl-pyrimidine with bacteriostatic and antiprotozoal properties. As a dihydrofolate reductase inhibitor, trimethoprim binds tightly to the bacterial enzyme, blocking the production of tetrahydrofolic acid from dihydrofolic acid, arresting folic acid synthesis.
    When Trimethroprim is combined with sulfonamides, like Sulfamethoxazole (S045), the two compounds show bactericidal effects, but are only bacteriostatic when used separately. The activity is attributed to their synergistic effect in inhibiting folic acid metabolism in bacteria.
    Trimethoprim has a wide antibacterial spectrum and is active against most Gram-positive and Gram-negative aerobic bacteria, including Nocardia, Brucella, Gram-negative bacilli, and some Gram-positive bacteria like Streptococcus, Toxoplasma and some other coccidians. It is used to treat recurrent cystitis, mild acute prostatitis, urinary tract infections, asymptomatic bacteriuria during pregnancy and respiratory tract infections. The product is very slightly soluble in aqueous solution.
    
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    Background
    
    Trimethoprim interferes with the cellular metabolism of folic acid in the bacterial cell by blocking the biosynthesis of nucleotides. Trimethoprim binds to dihydrofolate reductase and inhibits the reduction of dihydrofolic acid to tetrahydrofolic acid. Tetrahydrofolic acid is an essential precursor in the thymidine synthesis pathway and interference with this pathway inhibits bacterial DNA synthesis.
- Properties
  - CAS Number
    
    738-70-5
    
    Molecular Formula
    
    C14H18N4O3
    
    Molecular Weight
    
    290.32
    
    Appearance
    
    White or yellowish-white powder
    
    Other Properties
    
    Assay (On Dried Basis): 98.5 - 101.0%
    Residue On Ignition: Not more than 0.1%
    Loss on Drying: Not more than 0.5%
    Melting Point: 199°C - 203°C
    Identification: USP, A and B
    
    Storage
    
    2-8 °C
    
    * For research use only
- Applications
  - Application Description
    
    Spectrum: Trimethoprim has a wide antibacterial spectrum and is active against most gram-positive and gram-negative aerobic bacteria, including Nocardia, Brucella, Gram-negative bacilli, and some Gram-positive bacteria like Streptococcus, Toxoplasma and some other coccidians. It is used to treat recurrent cystitis, mild acute prostatitis, urinary tract infections, asymptomatic bacteriuria during pregnancy and respiratory tract infections.
    
    Microbiology Applications: Trimethoprim is commonly used in clinical in vitro microbiological antimicrobial susceptibility tests (panels, discs, and MIC strips) against Gram-positive and Gram-negative microbial isolates. Medical microbiologists use AST results to recommend antibiotic treatment options. Representative MIC values include:
    Escherichia coli 0.25 µg/mL - 64 µg/mL
    Haemophilus influenzae 0.15 µg/mL - 16 µg/mL
    Media Supplement
    Trimethoprim can be used as a selective agent in several types of isolation media:
    Columbia Blood Agar - Campylobacter selective supplement (Skirrow)
    Columbia Blood Agar - Campylobacter selective supplement (Blaser-Wang)
    Campylobacter Agar - Campylobacter Selective Supplement (Preston)
    Columbia Blood Agar - Helicobacter pylori Selective Supplement (Dent)
    Bolton Broth - Bolton Broth Selective Supplement
    Campylobacter Agar Base - Modified Preston Campylobacter Selective Supplement
    Bolton Broth - Modified Bolton Broth Selective Supplement
    ChromogenicBacillus cereus Agar - Chromogenic Bacillus cereus Selective Supplement
    
    Plant Biology Applications: Trimethoprim can be used in combination with rifampicin to provide sufficient coverage against pathogenic microbes. When used without other supplemental antibiotics, Trimethoprim was not shown to provide sufficient coverage (Pollock et al, 1983).