Child: ≥6 months 10 mg/kg daily in divided doses 12 hourly for 10 days. Treatment recommendations may vary among individual products and between countries (refer to specific product guidelines).
Adult: Acute infection: 100 mg or 200 mg bid. Alternatively, 200 mg or 300 mg once daily as a single dose. Treatment duration is based on the nature and severity of the infection. Dosing recommendations may vary among individual products and between countries (refer to specific product guidelines). Child: Acute infection: 6 weeks to 5 months 25 mg bid; 6 months to 5 years 50 mg bid; 6-12 years 100 mg bid; >12 years Same as adult dose. Treatment and dosing recommendations may vary among individual products and between countries (refer to specific product guidelines). Elderly: Dose reduction may be required.
Oral Prophylaxis of recurrent urinary tract infections
Adult: Long-term treatment: 100 mg once daily at night. Treatment duration may vary among individual products and between countries (refer to specific product guidelines). Child: Long-term treatment: 6 months to 5 years 25 mg once daily at night; 6-12 years 50 mg once daily at night; >12 years Same as adult dose. Treatment and dosing recommendations may vary among individual products and between countries (refer to specific product guidelines). Elderly: Dose reduction may be required.
Treatment and dosing recommendations may vary among individual products and between countries (refer to specific product guidelines).
Administration
Should be taken with food.
Contraindications
Hypersensitivity. Megaloblastic anaemia due to folate deficiency and other blood dyscrasias.
Special Precautions
Patient at risk of developing hyperkalaemia (e.g. poorly controlled diabetes mellitus, hypoaldosteronism; concomitant use K-sparing diuretics, K supplements, K-containing salt substitutes, renin-angiotensin system inhibitors, heparin); acute porphyria; with potential folate deficiency (e.g. malnourished, chronic anticonvulsant therapy). Not indicated for prophylactic or prolonged administration at any age (when used in otitis media). Renal and hepatic impairment. Children and elderly. Pregnancy and lactation.
Adverse Reactions
Significant: Depression of haemopoiesis, hyperkalaemia; Clostridium difficile-associated diarrhoea. Rarely, serious hypersensitivity reaction. Blood and lymphatic system disorders: Thrombocytopenia, leucopenia, neutropenia, megaloblastic anaemia, methemoglobinaemia. Gastrointestinal disorders: Diarrhoea, nausea, vomiting. Infections and infestations: Monilial overgrowth. Metabolism and nutrition disorders: Hyponatraemia. Nervous system disorders: Headache. Skin and subcutaneous tissue disorders: Rash, urticaria, pruritus, exfoliative dermatitis.
Perform culture and susceptibility tests; consult local institutional recommendations before treatment initiation due to antibiotic resistance risks. Obtain LFTs before initiating therapy. Monitor CBC with differential, platelet count, bilirubin, serum creatinine or K; BUN at baseline and periodically during therapy (particularly when using high doses or in prolonged treatment).
Overdosage
Symptoms: Acute: Nausea, vomiting, headache, dizziness, mental depression, confusion, bone marrow depression. Chronic: Bone marrow depression manifested as thrombocytopenia, leucopenia, megaloblastic anaemia. Management: Symptomatic and supportive treatment. Acute: Perform gastric lavage and forced diuresis. May give IM calcium folinate for depression of haematopoiesis. Enhance elimination through urine acidification. Chronic: May administer leucovorin.
Drug Interactions
Increased risk of hyperkalaemia with K-sparing diuretics, K supplements, K-containing salt substitutes, renin angiotensin system inhibitors (e.g. ACE inhibitors, renin-angiotensin receptor blockers), other drugs associated with increase in serum K (e.g. heparin). May induce folate deficiency with folate antagonists or anticonvulsants. Increased serum concentration with dapsone. Increased risk of haematologic toxicity with cytotoxic drugs (e.g. azathioprine, mercaptopurine, methotrexate). Increased incidence of thrombocytopenia with purpura with diuretics (particularly thiazides). Increased risk of nephrotoxicity with ciclosporin. Increased antifolate effect with pyrimethamine. May enhance hypoglycaemic effects of repaglinide. May potentiate anticoagulant effect of warfarin and other coumarins. May increase serum concentration of lamivudine, phenytoin, procainamide, digoxin, dapsone, zidovudine. May decrease serum concentration with rifampicin.
Lab Interference
May interfere with the Jaffe alkaline picrate reaction assay resulting in a falsely increased (approx 10%) creatinine. May interfere with the determination of serum methotrexate when a bacterial dihydrofolate reductase is used as the binding protein (e.g. competitive binding protein technique) in the assay.
Action
Description: Trimethoprim, a diaminopyrimidine, is a reversible inhibitor of dihydrofolate reductase. It inhibits the conversion of bacterial dihydrofolate reductase to tetrahydrofolic acid, necessary for the synthesis of nucleic acids and proteins. It may be bactericidal or bacteriostatic depending on growth conditions. Pharmacokinetics: Absorption: Rapidly and almost completely absorbed from the gastrointestinal tract. Time to peak plasma concentration: Approx 1-4 hours. Distribution: Widely distributed to various tissue and fluids (e.g. kidneys, liver, lung, bronchial secretions, aqueous humour, saliva, prostatic tissue and fluid, vaginal secretions); present in CSF. Crosses the placenta and enters breast milk. Volume of distribution: Approx 1.3 L/kg. Plasma protein binding: Approx 45%. Metabolism: Partially metabolised (10-20%) in the liver via demethylation, oxidation, hydroxylation. Excretion: Primarily via urine (50-60%; 80% as unchanged drug); faeces. Elimination half-life: Approx 8-10 hours.
Chemical Structure
Trimethoprim Source: National Center for Biotechnology Information. PubChem Compound Summary for CID 5578, Trimethoprim. https://pubchem.ncbi.nlm.nih.gov/compound/Trimethoprim. Accessed Apr. 27, 2022.
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