Trimethoprim

• Mechanism of Action
• Inhibits the production of dihydrofolate reductase (DHFR), resulting in reduced conversion of dihydrofolic acid to active tetrahydrofolic acid - interfering with bacterial synthesis of nucleic acids.
• • Pharmacology
  • Higher affinity for bacterial dihydrofolate reductase than for human DHFR.
  • Mostly excreted unmetabolised into urine in high concentrations, resulting in its effect directly within the bladder.
• • Microbiology
  • Active against most GI normal flora, the most common cause of UTI.

Clinical Use

• • Indication
  • Uncomplicated symptomatic urinary tract infection.
• • Contraindications
  • Megaloblastic anaemia due to folate deficiency.
• • Adverse Effects
  • Rash / pruritis
  • Nausea / vomiting
  • Elevated LFTs