Medicines & Supplements A to Z > Trimethoprim


Last updated on 06/07/2021.

Overview   |   Dosage   |    Side Effects   |   Precautions  |   Tips  |   Where To Buy  

GENERIC NAME: Trimethoprim



BRAND NAME(S) IN HONG KONG: Trimoprim, Suprim

DRUG CLASS: Antibiotics

SUB CLASS: Folic acid antagonist

USED FOR: Acute otitis media, susceptible infections, urinary tract infections (UTIs)

– 80 mg (Tablets)
– 50 mg/5ml (Suspension)

What is Trimethoprim for?

Trimethoprim belongs to a class of medications called folic acid antagonists. It kills bacteria by inhibiting DNA synthesis and replication. Trimethoprim is used to treat urinary tract infections. Trimethoprim does not work for virus or fungus infections.

Trimethoprim is usually found in combination with Sulfamethoxazole for the treatment of certain types of pneumonia.

How to use it?

Trimethoprim is available as tablets and suspensions, which are taken by mouth. Oral Trimethoprim should be taken with food.

Acute otitis media
Child over 6 months
10 mg/kg body weight daily in 2 divided doses for every 12 hours, for 10 days.

Susceptible infections, urinary tract infections
100 mg or 200 mg twice daily for 3-14 days.
Child 6-12 years
100 mg twice daily.
Child 2-6 years
50 mg twice daily.
Child over 4 months
6 mg/kg body weight daily in 2 divided doses.

Prevention of recurrent urinary tract infections
100 mg once at night.
Child 8-12 years
100 mg once at night.
Child 2-8 years
50 mg once at night.
Child over 4 months
2 mg/kg body weight once at night.

What are the side effects of Trimethoprim?

Common side effects of Trimethoprim include diarrhoea, fungal infection, dizziness, headache, nausea and vomiting, and allergic skin reactions.

Who should not take Trimethoprim?

– People allergic to Trimethoprim or any component of the formulation.
– Patients with a history of megaloblastic anemia due to folate deficiency.

Pharmacist Tips:

– Trimethoprim should be taken with food to minimize gastrointestinal discomfort.

Common dosing schedule:
Once or twice daily, taken with food.

This schedule is for reference only, adjustments may be made according to individual needs.

Some common medications Trimethoprim may interact with:
– Other folate acid antagonists, e.g. Pyrimethamine, Methotrexate
– Angiotensin converting enzyme inhibitors, e.g. Captopril, Lisinopril
Ciclosporin, Dapsone, Phenytoin, Digoxin, Procainamide

Please notify your doctor or pharmacist if you are taking the above medication, dosage adjustments might be needed.

Where to buy Trimethoprim in Hong Kong?

In Hong Kong, Trimethoprim is a prescription only medicine, and requires a prescription from a doctor to be purchased in a pharmacy. It can also be obtained from doctors. To find a pharmacy near you, refer to the list of pharmacies (“Authorized Sellers of Poisons”) from the Hong Kong Department of Health.

For more information about drug names and ingredients, you can visit Hong Kong’s Drug Office at

Need more information?

For detailed information about the use of Trimethoprim in children, pregnancy and breastfeeding, and for questions about drug interactions, please check with your pharmacist or doctor.

Disclaimer: our goal is to provide you with the most relevant drug information and common dosage for Hong Kong. This information does not constitute medical advice. For specific treatment recommendations and advice, always discuss with your doctor or pharmacist, and follow the instructions included with your specific medicine.