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Antibiotic Dosing in CKD Pregnancy: Trimethoprim is contra-indicated in pregnant women, premature infants or infants during the first few weeks of life. Trimethoprim is contraindicated during the first trimester of pregnancy (see section 4.3). Studies in animals have shown a teratogenic effect. Epidemiological studies have shown an increased risk of spontaneous abortion and congenital malformations, in particular neural tube defects, oral clefts and cardiovascular defects, in children of mothers treated with trimethoprim during the first trimester of pregnancy. The presumed mechanism of action is thought to be interference with folates. In the second and third trimesters, use should be avoided, unless clinically necessary. Breastfeeding: Trimethoprim is excreted in breast milk. Effects on the suckling child are likely if therapeutic doses are administered to breast-feeding mothers. Trimethoprim is contraindicated if the breast fed infant is less than 4 months of age.

Trimethoprim (CKD Considerations)

Brand names: Monotrim

Trimethoprim, a common antibacterial for urinary tract infection, considered in the context of chronic kidney disease where dosing and electrolyte effects need attention. The focus here is safe use when renal function is impaired.

Adult dose

Dose: Adults and children over 12 years, eGFR over 30 ml/min (normal dose) — treatment of urinary tract infections and all other susceptible infections: 200 mg (20 ml) twice daily; long-term prevention of recurrent urinary tract infections: 100 mg (10 ml) at night. Reduced kidney function (SPC table, by eGFR in ml/min): 15–30 — normal dose for 3 days then half dose; under 15 — half the normal dose.
Route: Oral (oral suspension 50 mg/5 ml)
Frequency: Treatment: twice daily. Long-term prevention: once, at night. Reduced eGFR: see dose.
The pinned product's §4.2 prints a renal dosage table (eGFR over 30 / 15–30 / under 15) plus dialysis and monitoring statements, and §4.1 covers urinary tract infections and other susceptible infections, so the page's CKD use is covered and a dose is written. SCOPE: pinned product is the 50 mg/5 ml oral SUSPENSION (doses printed in mg with the equivalent volume). The label prints the half-dose steps only in words ('half dose', 'half the normal dose'); no milligram figure for them is written here, and no duration or maximum dose is printed in the retrieved §4.2. CKD-RELEVANT SAFETY TEXT FROM THIS SPC: hyperkalaemia is very common (§4.8) and patients at risk include those with renal insufficiency (§4.4); "Trimethoprim should only be initiated and used in dialysis patients under close supervision from specialists in both infectious disease and renal medicine. Trimethoprim is removed by dialysis." Concomitant ciclosporin: increased risk of nephrotoxicity (§4.5). NOT ASSERTED: the retrieved SPC text does not state that trimethoprim raises serum creatinine without a change in GFR (§4.8 was cut off before any renal and urinary disorders section), so nothing about creatinine interference is written from this source. paedDose is null: the label's paediatric figures are for urinary tract infection and carry no renal-impairment split, so they are not carried onto this CKD page; use a children's formulary.

Dose adjustments

Renal

SPC §4.2, 'Dosage advised where there is reduced kidney function' by eGFR (ml/min): over 30 — normal dose; 15–30 — "Normal for 3 days then half dose"; under 15 — "Half the normal dose". "Monitoring of renal function and serum electrolytes should be considered particularly with longer term use, in patients with impaired renal function." "Trimethoprim should only be initiated and used in dialysis patients under close supervision from specialists in both infectious disease and renal medicine. Trimethoprim is removed by dialysis." "Monitoring trimethoprim plasma concentration may be considered with long term therapy but the value of this in individual cases should first be discussed with specialists in infectious disease and renal medicine." Elderly: "Depending on kidney function, see special dosage schedule." §4.4: "In patients with renal impairment, care should be taken to avoid accumulation." No numeric half-dose is printed (the label says only 'half dose' / 'half the normal dose'), so none is calculated here.

Hepatic

Trimethoprim is contra-indicated in severe hepatic insufficiency (§4.3). The retrieved §4.2 prints no dose adjustment for lesser degrees of hepatic impairment. §4.8 reports that "Fatalities have been reported (especially in the elderly, or those with impairment of renal or hepatic function" for the blood and lymphatic reactions, so careful monitoring is advised in those patients.

Dose independently re-sourced from UK Summary of Product Characteristics (SPC) via the eMC — clinician-reviewed. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

  • Hypersensitivity to the active substance or to any of the excipients listed in section 6.1 (§4.3).
  • Severe hepatic insufficiency (§4.3).
  • Megaloblastic anaemia and other blood dyscrasias (§4.3).
  • Pregnant women (§4.3: first trimester of pregnancy; §4.6: contra-indicated in pregnant women, and in the second and third trimesters use should be avoided unless clinically necessary), premature infants and neonates under 6 weeks (§4.3).
  • Breast-fed infant less than 4 months of age (§4.6: "Trimethoprim is contraindicated if the breast fed infant is less than 4 months of age").
  • Known or suspected risk of acute porphyria: treatment should be avoided (§4.4 warning, not listed in §4.3).
  • Previous serious reaction (SJS, TEN or DRESS) to trimethoprim: "the treatment must not be restarted in this patient at any time" (§4.4).
  • Hereditary fructose intolerance: "Patients with rare hereditary problems of fructose intolerance should not take this medicine" (§4.4; this product is the oral suspension).

Side effects

  • Very common: hyperkalaemia. Elderly patients and those taking high doses "may be more susceptible to hyperkalaemia and hyponatraemia" (§4.8).
  • Common: monilial overgrowth; headache; nausea, diarrhoea, vomiting; skin rashes, urticaria (§4.8).
  • Blood and lymphatic (very rare): leucopenia, neutropenia, thrombocytopenia, pancytopaenia, bone marrow depression, agranulocytosis, aplastic anaemia, haemolytic anaemia, eosinophilia, purpura, haemolysis; (not known): megaloblastic anaemia, methaemoglobinaemia, depression of haematopoiesis. Fatalities have been reported, especially in the elderly or those with renal or hepatic impairment; most haematological changes are mild and reversible when treatment is stopped (§4.8).
  • Immune (very rare): hypersensitivity, anaphylaxis, angioedema, drug fever, allergic vasculitis resembling Henoch-Schoenlein purpura, periarteritis nodosa, systemic lupus erythematosus (§4.8).
  • Metabolism (very rare): hypoglycaemia, hyponatraemia, anorexia (§4.8).
  • Psychiatric (very rare): depression, hallucinations, confusional states, agitation, anxiety, abnormal behaviour, insomnia and nightmares (§4.8).
  • Nervous system and sensory (very rare): dyskinesias, aseptic meningitis (rapidly reversible on withdrawal but recurred on re-exposure to co-trimoxazole or trimethoprim alone), tremor, ataxia, dizziness, lethargy, syncope, paraesthesiae, convulsions, peripheral neuritis, vertigo, tinnitus; uveitis (§4.8).
  • Respiratory (very rare): cough, shortness of breath, wheeze, epistaxis (§4.8).
  • Gastrointestinal (very rare): constipation, glossitis, stomatitis, pseudomembranous colitis, pancreatitis; (not known): sore mouth, gastro-intestinal disturbance (§4.8).
  • Hepatobiliary (very rare): elevation of serum transaminases, elevation of bilirubin levels, cholestatic jaundice, hepatic necrosis; cholestatic jaundice and hepatic necrosis may be fatal (§4.8).
  • Skin (very rare): photosensitivity, exfoliative dermatitis, fixed drug eruption, erythema multiforme, erythema nodosum, Stevens-Johnson syndrome, toxic epidermal necrolysis, bullous dermatitis, purpura; (not known): pruritus, drug reaction with eosinophilia and systemic symptoms (DRESS). Toxic epidermal necrolysis "carries a high mortality" (§4.8).
  • §4.8 is truncated at the source-fetch limit after the skin disorders; the musculoskeletal and any later system-organ classes were not retrieved.

Interactions

  • Folate antagonists and anticonvulsants: trimethoprim may induce folate deficiency in predisposed patients, such as those receiving concomitant folate antagonists or anticonvulsants (§4.5).
  • Bone marrow depressants: may increase the potential for bone marrow aplasia; cytotoxics such as azathioprine, mercaptopurine and methotrexate increase the risk of haematologic toxicity; special care with pyrimethamine (§4.5).
  • Phenytoin and digoxin: trimethoprim may increase their plasma concentrations by increasing their elimination half-life; careful monitoring advised (§4.5).
  • Rifampicin may decrease trimethoprim concentrations (§4.5).
  • Diuretics (primarily thiazides) in elderly patients: increased incidence of thrombocytopenia with purpura (§4.5).
  • Drugs that increase serum potassium (potassium-sparing diuretics, potassium supplements, potassium-containing salt substitutes, renin-angiotensin system inhibitors such as ACE inhibitors or angiotensin receptor blockers, heparin): may lead to a significant increase in serum potassium; monitor potassium (§4.4, §4.5).
  • Ciclosporin: increased risk of nephrotoxicity (§4.5).
  • Procainamide: trimethoprim increases plasma concentrations of procainamide (§4.5).
  • Dapsone: plasma concentrations of trimethoprim and dapsone may increase when taken together (§4.5).
  • Repaglinide: trimethoprim may enhance the hypoglycaemic effects of repaglinide; blood glucose monitoring advised (§4.4, §4.5).
  • Warfarin and other coumarins: trimethoprim may potentiate the anticoagulant effect (§4.5).
  • Pyrimethamine: increased antifolate effect (§4.5).

Monitoring

  • Regular haematological tests during long-term therapy and in patients predisposed to folate deficiency (e.g. the elderly), to check for possible pancytopaenia; particular care with haematological monitoring in children on long-term therapy (§4.4). If there is evidence of folic acid deficiency, calcium folinate should be given and response checked by haematologic monitoring (§4.4).
  • Renal function and serum electrolytes: monitoring "should be considered particularly with longer term use, in patients with impaired renal function" (§4.2, §4.4).
  • Serum potassium: close monitoring in patients at risk of hyperkalaemia (renal insufficiency, poorly controlled diabetes mellitus, potassium-sparing diuretics, potassium supplements, potassium-containing salt substitutes, renin angiotensin system inhibitors, heparin) (§4.4).
  • Blood glucose if co-administered with repaglinide (§4.4).
  • Skin: monitor closely for severe cutaneous reactions (SJS, TEN, DRESS); withdraw trimethoprim immediately if signs appear (§4.4).
  • Trimethoprim plasma concentration may be considered with long-term therapy, after discussion with specialists in infectious disease and renal medicine (§4.2).

Clinical monograph

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.

Reference: NICE NG109 (UTI Adults); MHRA guidance; PHE Antimicrobial Resistance Reports; SPC Monotrim; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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