Trimethoprim (CKD Considerations)

How it works

It inhibits bacterial dihydrofolate reductase, blocking folate synthesis and bacterial DNA production. It is predominantly renally excreted, so clearance falls as renal function declines.

Prescribing in practice

• Trimethoprim raises serum potassium and creatinine and can cause dangerous hyperkalaemia in CKD, particularly with ACE inhibitors, ARBs or potassium-sparing diuretics — check renal function and potassium and reduce frequency in significant impairment.
• The creatinine rise is partly a benign block of tubular secretion, but true acute kidney injury must still be excluded if function worsens.
• Avoid combining with methotrexate and use cautiously with other folate antagonists owing to additive marrow toxicity; consult current prescribing references for renal dose adjustment.

Monitoring

Check renal function and serum potassium where treatment is prolonged, doses are higher, or interacting drugs or significant CKD are present.

Counselling the patient

• Complete the full course as prescribed even once you feel better.
• Tell your prescriber about kidney problems or other medicines that affect potassium.
• Report palpitations, muscle weakness or feeling generally unwell.

Evidence & guidelines

NICE and MHRA guidance highlight the hyperkalaemia and acute kidney injury risk of trimethoprim with renin-angiotensin blockers, especially in older or CKD patients.