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Trimethoprim
Trimethoprim is a bacteriostatic antibioticmainly used in the prophylaxisand treatment of urinary tract infections (cystitis). It belongs to the class of chemotherapeuticagents known as dihydrofolate reductaseinhibitors. Trimethoprim was formerly marketed by GlaxoWellcomeunder trade names including Proloprim®, Monotrim® and Triprim®; but these trade names have been licensed to various generic pharmaceuticalmanufacturers.
Mechanism of actionTrimethoprim acts by interfering with the action of bacterial dihydrofolate reductase, inhibiting synthesis of tetrahydrofolic acid. Folic acid is an essential precursor in the de novo synthesis of the DNA nucleosides thymidineand uridine. Bacteria are unable to take up folic acid from the environment (i.e. the infection host) thus are dependent on their own de novo synthesis - inhibition of the enzyme starves the bacteria of two bases necessary for DNAreplicationand transcription. Image:THFsynthesispathway.png Co-trimoxazoleTrimethoprim is commonly used in combination with sulfamethoxazole, a sulfonamideantibiotic, which inhibits the an earlier step in the folate synthesis pathway (see diagram above). This combination, known as co-trimoxazole, results in a synergistic antibacterial effect by inhibiting successive steps in folate synthesis. Its use has been declining due to reports of sulfamethoxazole bone marrowtoxicity. Clinical indicationsTrimethoprim, used as monotherapy, is indicated for the prophylaxis and treatment of urinary tract infections(cystitis). Co-trimoxazole, owing to its greater efficacy, is indicated for a wider range of infections. For example, it is used as prophylaxis in patients at risk for Pneumocystis jiroveci pneumonia(e.g. AIDSpatients and those with some hematological malignancies), as therapy in Whipple's diseaseand certain other infections. External links
Categories: Antibiotics| Dihydrofolate reductase inhibitors
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