Medicines & Supplements A to Z > Co-trimoxazole


Last updated on 02/07/2021.

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

GENERIC NAME: Sulfamethoxazole + Trimethoprim



DRUG CLASS: Antibiotics

SUB CLASS: Folic acid antagonist, Sulfonamides

USED FOR: Pneumonia, bronchitis, Traveller’s diarrhoea, urinary tract infections (UTIs)

– 480 mg, 960 mg (tablets)
– 480 mg (capsules)
– 240 mg/5ml (suspension)
– 480 mg (injections)

What is Co-trimoxazole for?

Co-trimoxazole is a combination antibiotic of two antibacterial medicines – Trimethoprim and a sulfonamide medicine called Sulfamethoxazole. Both medications have synergistic activity and work by inhibiting the growth of bacteria. Co-trimoxazole is used to treat various bacterial infections, such as traveller’s diarrhoea, pneumonia, bronchitis and infections of the urinary tract, ears, and intestines.

How to use it?

Co-trimoxazole is available as tablets, capsules and suspensions which are taken orally with food. It is usually given 2-4 times daily.

Traveller’s diarrhoea
Sulfamethoxazole 800 mg + Trimethoprim 160 mg taken by mouth every 12 hours for 5 days.

Urinary tract infections
Sulfamethoxazole 800 mg + Trimethoprim 160 mg taken by mouth twice daily for 3 days.
Sulfamethoxazole 40 mg per kg body weight, plus Trimethoprim 8 mg/kg body weight per day, divided every 12 hours. Taken by mouth for 10 days.

What are the side effects of Co-trimoxazole?

Common side effects of Co-trimoxazole include headache, diarrhoea and nausea. Report to your doctor immediately and do not take any more if you experience skin rash or itchiness.

Who should not take Co-trimoxazole?

– People allergic to Co-trimoxazole or any component of the formulation.
– People who are allergic to sulfonamide medications.
– Infants younger than 2 months of age.
– Patients with reduced liver function or liver failure.
– Patients with a history of megaloblastic anemia due to folate deficiency.

Pharmacist Tips:

– This medication may cause photosensitivity. Use sunscreen and avoid tanning beds and prolonged exposure to sunlight.
– If you experience symptoms like skin rash or blistering of skin, report to your doctor immediately.
– Drink plenty of water to replace any lost fluids due to diarrhoea.

Common dosing schedule:
Co-trimoxazole should be taken every 12 hours, once in the morning and once at bedtime. Co-trimoxazole is best taken with food or a drink.

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

Some common medications Co-trimoxazole may interact with:
– Antibiotics, e.g. Dapsone, Sulfonamides

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

Where to buy Co-trimoxazole in Hong Kong?

In Hong Kong, Co-trimoxazole 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

For detailed information about the use of alprazolam 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.