NZ Formulary

Trimethoprim and sulfamethoxazole

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

What does it do?

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

How should you take it?

Take trimethoprim and sulfamethoxazole regularly as directed. Keep taking it until the course is finished, even if you start to feel better.
Take the tablets with a glass of water.
Measure the liquid 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?

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

Important information continues on next page.

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

Tell your doctor immediately

Diarrhoea, vomiting, nausea, loss of appetite


More sensitive to sunlight (sunburn or rash)

Tell your doctor if troublesome

Stomach upset

Take with food

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

Other information:

  • 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.
  • Protect yourself from too much sunlight while being treated with trimethoprim and sulfamethoxazole. Always cover up and apply a thick layer of broad spectrum sunscreen (at least SPF 30) when outside. Do not use sunbeds.