How do you take Sulfamethoxazole; Trimethoprim?

For most infections, the usual adult dose is 2 regular-strength tablets (each containing 400mg sulfamethoxazole and 80mg trimethoprim) taken every 12 hours, which means one dose in the morning and one in the evening. Take with a full glass of water and drink plenty of water throughout the day to protect your kidneys. You can take it with or without food, but taking it with food can reduce stomach upset.

What are the side effects of Sulfamethoxazole; Trimethoprim?

Nausea or vomiting, loss of appetite, mild skin rash, diarrhea, headache

Who should not take Sulfamethoxazole; Trimethoprim?

People allergic to sulfonamide drugs (sulfa drugs) or trimethoprim, babies under 2 months old, people with severe liver or kidney disease, people with a blood disorder called megaloblastic anaemia caused by folate deficiency, and people with a condition called G6PD deficiency (a blood condition that is common in Nigeria).

Prescription

Antibiotic (Sulfonamide combination)

Sulfamethoxazole; Trimethoprim

Last reviewed July 2026

Who is this for?

For adults (18+). Standard adult dosing applies: see the How to Take tab for full instructions.

What is this drug?

Sulfamethoxazole/Trimethoprim (commonly called Co-trimoxazole or Septrin) is a combination antibiotic that contains two medicines working together to kill bacteria by blocking two different steps they need to grow and multiply.

How it works

Inhibits bacterial dihydrofolate reductase (trimethoprim) and dihydropteroate synthase (sulfamethoxazole), blocking sequential steps in folate synthesis and preventing bacterial DNA replication and cell division.

What is it used for?

Urinary tract infections (urine infections), typhoid, ear infections, chest infections (bronchitis, pneumonia), diarrhea caused by bacteria, skin infections, and prevention of infections in people with weak immune systems including HIV patients

Browse by condition

Typhoid Ear Infections Throat & Chest Infections Urinary Tract Infection (UTI)Diarrhea & Dysentery HIV & AIDS Skin Infections Kidney & Urinary Bacterial Infections

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What to watch out for

Always complete the full course of this antibiotic even if you start feeling better, as stopping early can make the infection come back stronger and harder to treat. Drink plenty of water while taking this drug to protect your kidneys, especially in hot Nigerian weather. Buy only from licensed pharmacies and do not buy Co-trimoxazole from roadside vendors or open markets as fake and expired versions are common and can be dangerous.

Common Side Effects

Nausea or vomiting
loss of appetite
mild skin rash
diarrhea
headache

Serious Side Effects

Severe skin rash with peeling or blisters (this is an emergency: stop the drug and go to the hospital immediately)
unusual bleeding or bruising
yellowing of the eyes or skin (sign of liver problems). If you notice any of these
seek medical help right away.

Drug Interactions

Avoid taking with methotrexate (used for arthritis and cancer) as it can cause dangerous blood problems. Be careful if you are taking blood-thinning medicines like warfarin, as Co-trimoxazole can increase the risk of bleeding. Avoid alcohol while taking this drug as it may increase the chance of side effects and reduce how well the medicine works.

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Pregnancy & Breastfeeding Warning

This drug is NOT safe during pregnancy, especially in the first three months and near delivery, and should be used with caution during breastfeeding. Always consult your doctor before taking it if you are pregnant, planning to become pregnant, or breastfeeding.

Who Should NOT Take This

People allergic to sulfonamide drugs (sulfa drugs) or trimethoprim
babies under 2 months old
people with severe liver or kidney disease
people with a blood disorder called megaloblastic anaemia caused by folate deficiency
and people with a condition called G6PD deficiency (a blood condition that is common in Nigeria).

How to Store

Store in a cool, dry place away from direct sunlight and heat. Nigerian weather can be very hot, so avoid leaving it on window sills or inside hot cars. Keep the bottle or pack tightly closed to protect from humidity. Always keep out of reach of children. Suspension should be used within the period stated on the label after opening.

For information only: not medical advice. Always talk to a doctor or pharmacist before changing your medication.