NZ Formulary

Trimethoprim and sulfamethoxazole

try-meth-oh-prim and sul-fah-meth-ox-ah-zole

What does it do?

Trimethoprim and sulfamethoxazole is an antibiotic used to treat and prevent bacterial infections.

Before you start

  • Tell your doctor if you have an allergy to ‘sulfa’ medicines, if you have kidney, liver or blood problems, or if you have G6PD deficiency.
  • Tell your doctor if you are pregnant, planning to become pregnant, or breastfeeding.

How should you take it?

Take trimethoprim and sulfamethoxazole regularly as directed. You can take it with or without food. Keep taking it until the course is finished, even if you start to feel better.
Tablet: Take with a glass of water.
Liquid: Measure carefully with an oral syringe or measuring spoon. Shake the bottle well before measuring each dose.

What if you forget a dose?

Take the missed dose as soon as possible and continue as directed.

Can you take other medicines?

Some medicines available without a prescription may react with trimethoprim and sulfamethoxazole including:

  • potassium supplements (e.g. Span K®)

Tell your pharmacist or doctor about all medicines or treatments that you may be taking, including vitamins, herbal products or recreational drugs.

What side effects might you notice?

Side EffectsRecommended action

Skin rash, skin peeling or blisters

Stop taking and see your doctor immediately

Severe headache, stiff neck, confusion, eyes sensitive to light

Reduced number of blood cells that fight infections or help your blood to clot - symptoms include: fever, chills, sore throat or generally feeling unwell, or easy or unusual bruising or bleeding

Symptoms of liver problems including: yellow skin or eyes, itching, dark urine, pale bowel motions, abdominal pain

Severe stomach pain, nausea

Tell your doctor immediately

Changes in heartbeat, muscle cramps or weakness

Tell your doctor

Stomach upset

Tell your doctor if troublesome

If you notice any other effects, discuss them with your doctor or pharmacist.