Trimethoprim

• inhibits dihydrofolate reductase, preventing conversion of dihydrofolate to tetrahydrofolate

• prevents synthesis of thymidine, some purines, methionine and glycine

• commonly used in combination with sulfamethoxazole

  • for treatment of Pneumocystis carinii infection

• do NOT use in pregnancy

Activity

Resistance

• decreased affinity of dihydrofolate reductase

• enterococci use exogenous thymidine

Side Effects

• GI disturbances

• nausea and vomiting

• pruritus

• rashes

• Hyperkalaemia

• Depression of haematopoesis

Rarely

• Erythema Multiforme

• Toxic Epidermal Necrolysis

• photosensitivity

• allergic reactions

  • angioedema

  • anaphylaxis

• aseptic meningitis