15th March 2024

Trimethoprim

This agent is a dihydrofolate reductase inhibitor which disrupts bacterial folate synthesis. It has activity against gram-positive and gram-negative bacteria. It can be combined with sulphonamide or separately with sulfamethoxazole to make co-trimoxazole, which is used to treat and prevent Pneumocystis pneumonia (PCP).

Adverse effects include bone marrow suppression, folate deficiency and SJS. Concomitant use of this agent with other dihydrofolate reductase inhibitors, such as methotrexate, leads to synergistic folate antagonism. This can cause life-threatening myelosuppression and nephrotoxicity.