Generic Medicine Info
Indications and Dosage
Acute otitis media
Child: ≥6 mth: 10 mg/kg daily in 2 divided doses 12 hrly for 10 days.

Susceptible infections, Urinary tract infections
Adult: 100 or 200 mg bid, alternatively, 200 or 300 mg once daily for 3-14 days, depending on severity.
Child: 4 mth to 12 yr 6 mg/kg daily in 2 divided doses. Alternative regimen: 4 mth to 2 yr 25 mg bid; >2-6 yr 50 mg bid; >6-12 yr 100 mg bid.

Prophylaxis of recurrent urinary tract infections
Adult: 100 mg once daily at night.
Child: 4 mth to 12 yr 2 mg/kg once daily at night. Alternative regimen: 4 mth to 2 yr 25 mg at night; >2-8 yr 50 mg at night; >8-12 yr 100 mg at night.
Renal Impairment
 CrCl (mL/min)  Dosage
 <15  Not recommended.
 15-30   50 mg 12 hrly.
Should be taken with food.
Hypersensitivity. Blood dyscrasias (e.g. megaloblastic anaemia).
Special Precautions
Patient w/ actual or potential folate deficiency (e.g. malnourished, chronic anticonvulsant therapy, elderly). Hepatic and renal impairment. Childn (esp those w/ fragile X chromosome associated w/ mental retardation). Pregnancy and lactation.
Adverse Reactions
Pruritus, rash, urticaria, mild GI disturbance (e.g. nausea, vomiting, glossitis, sore mouth); disturbance of liver enzymes, photosensitivity, angioedema, myalgia, headache; hyperkalaemia, hyponatraemia; agranulocytosis. Rarely, fever, cholestatic jaundice, exfoliative dermatitis, anaphylaxis, aseptic meningitis, megaloblastic anaemia, thrombocytopenia, leucopenia, neutropenia, methaemoglobinaemia.
Potentially Fatal: Rarely, erythema multiforme, Stevens-Johnson syndrome, toxic epidermal necrolysis.
Monitoring Parameters
Monitor CBC w/ differential, platelet count, liver enzyme, bilirubin, serum K, serum creatinine, and BUN periodically during prolonged therapy.
Symptoms: Nausea, vomiting, dizziness, headache, mental depression, confusion, bone marrow depression (e.g. thrombocytopenia, leucopenia, megaloblastic anaemia). Management: Symptomatic and supportive treatment. May employ gastric lavage and forced diuresis. Enhance elimination through urine acidification. May administer Ca folinate (5-15 mg daily) if bone marrow depression occurs.
Drug Interactions
May increase concentration of dapsone. Increased elimination and shortened elimination half-life w/ rifampicin. Increases concentration of phenytoin, digoxin, procainamide, rosiglitazone, repaglinide, zidovudine, zalcitabine, lamivudine. Increased risk of nephrotoxicity w/ ciclosporin. Potentiates anticoagulant effect of warfarin. May cause hyponatraemia w/ diuretics. May cause megaloblastic anaemia w/ other folate inhibitors (e.g. pyrimethamine, methotrexate). May increase potential for bone marrow aplasia w/ bone barrow depressants. Increased risk of hyperkalaemia w/ ACE inhibitors.
Lab Interference
Interferes w/ serum methotrexate assay when used as binding protein for competitive binding protein technique (CBPA). May cause falsely elevated creatinine values w/ Jaffe alkaline picrate reaction assay.
Description: Trimethoprim, a diaminopyrimidine, is a reversible inhibitor of dihydrofolate reductase. It inhibits the conversion of bacterial dihydrofolic acid to tetrahydrofolic acid necessary for the synthesis of nucleic acids and proteins. It is either bacteriostatic or bacteriocidal, acting on the same metabolic pathway as sulfonamides.
Absorption: Rapidly and extensively absorbed from the GI tract. Time to peak plasma concentration: 1-4 hr.
Distribution: Widely distributed into body tissues and fluids. Readily 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, and hydroxylation.
Excretion: Via urine (approx 40-60%, mainly as unchanged drug) and faeces (small amounts). Elimination half-life: 8-10 hr.
Chemical Structure

Chemical Structure Image

Source: National Center for Biotechnology Information. PubChem Database. Trimethoprim, CID=5578, (accessed on Jan. 23, 2020)

Store between 15-25˚C. Protect from light.
MIMS Class
Other Antibiotics
ATC Classification
J01EA01 - trimethoprim ; Belongs to the class of trimethoprim and derivatives. Used in the systemic treatment of infections.
Anon. Trimethoprim. Lexicomp Online. Hudson, Ohio. Wolters Kluwer Clinical Drug Information, Inc. Accessed 15/07/2016.

Buckingham R (ed). Trimethoprim. Martindale: The Complete Drug Reference [online]. London. Pharmaceutical Press. Accessed 15/07/2016.

Joint Formulary Committee. Trimethoprim. British National Formulary [online]. London. BMJ Group and Pharmaceutical Press. Accessed 15/07/2016.

McEvoy GK, Snow EK, Miller J et al (eds). Trimethoprim. AHFS Drug Information (AHFS DI) [online]. American Society of Health-System Pharmacists (ASHP). Accessed 15/07/2016.

Primsol Solution (Aytu BioScience, Inc). DailyMed. Source: U.S. National Library of Medicine. Accessed 20/01/2017.

Trimethoprim Tablet (Gavis Pharmaceuticals, LLC). DailyMed. Source: U.S. National Library of Medicine. Accessed 15/07/2016.

Disclaimer: This information is independently developed by MIMS based on Trimethoprim from various references and is provided for your reference only. Therapeutic uses, prescribing information and product availability may vary between countries. Please refer to MIMS Product Monographs for specific and locally approved prescribing information. Although great effort has been made to ensure content accuracy, MIMS shall not be held responsible or liable for any claims or damages arising from the use or misuse of the information contained herein, its contents or omissions, or otherwise. Copyright © 2021 MIMS. All rights reserved. Powered by
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