Sounds like 'co-tri-mox-a-zole'

Key points about co-trimoxazole

  • Co-trimoxazole is an antibiotic used to treat different infections caused by bacteria.
  • Co-trimoxazole is also called Trisul or Deprim.
  • Find out how to take it safely and possible side effects. 
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Co-trimoxazole is an antibiotic that is used to treat bacterial infections such as bladder infections, skin infections or chest infections. It works by killing or stopping the growth of bugs that cause infection. It is not effective against infections caused by viruses. 

Co-trimoxazole is made up of two antibiotics (trimethoprim  and sulfamethoxazole). Sulfamethoxazole belongs to a group of antibiotics called sulphonamides

In Aotearoa New Zealand co-trimoxazole is available as tablets and liquid and can also be given as an injection in the hospital. 

  • The dose of co-trimoxazole will be different for different people depending on the type of infection and your age.
  • The usual dose for adults is 2 tablets twice a day.
  • The dose for children will depend on their body weight. It is usually given 2 times a day.
  • Your doctor will advise you how long to take co-trimoxazole for (usually 5 to 7 days) but for urinary tract infections, it may only be needed for 1 to 3 days.
  • Always take your co-trimoxazole exactly as your doctor has told you. The pharmacy label on your medicine will tell you how much to take, how often to take it and any special instructions.

Read more about the co-trimoxazole paediatric dose calculator.

  • Timing of your doses: Co-trimoxazole is usually taken 2 times a day. Try to space the doses evenly throughout the day such as the first thing in the morning and at bedtime. Ideally these times should be at 12 hours apart. Co-trimoxazole is best taken with food. Swallow the tablets with a drink of water. Do not chew them. 
  • Missed dose: If you forget to take your dose, take it as soon as you remember. But, if it is nearly time for your next dose, take the next dose at the right time. Do not take extra doses to make up for a forgotten dose.
  • Finish the course: It is important to take the whole course of antibiotics for the number of days your doctor has told you to. You should start to get better after taking co-trimoxazole for a few days. If you do not feel better or get more unwell, contact your doctor.

Here are some things to know when you're taking co-trimoxazole. Other things may be important as well, so ask your healthcare provider what you should know about.

  • Co-trimoxazole does not have direct interactions with alcohol. This means that most people could have the occasional drink while taking it without any serious problems. However, if co-trimoxazole makes you feel sick (nausea), do not drink alcohol as it will make you feel worse.
  • If you are taking the contraceptive pill, you do not usually need to use additional contraception if you're taking co-trimoxazole. But if the antibiotic or the illness they're treating cause diarrhoea or vomiting, lasting more than 24 hours, absorption of the contraceptive pill may be affected. If this happens, ask your doctor or pharmacist for advice about contraception over the following few days.

Like all medicines, co-trimoxazole can cause side effects, although not everyone gets them. Often side effects improve as your body gets used to the new medicine.

Side effects What should I do?
  • Nausea (feeling sick) or vomiting
  • Try taking co-trimoxazole with food.
  • Diarrhoea (loose, watery stools)
  • This may settle after a few days.
  • Tell your doctor if troublesome or if you become dehydrated.
  • Vaginal itching, soreness or discharge (thrush)
  • Mouth ulcers
  • Tell your doctor or pharmacist.
  • Allergic reaction such as skin rash, itching, swelling of the lips, face, and mouth or difficulty breathing
  • Stop taking co-trimoxazole.
  • Tell your doctor immediately or ring Healthline 0800 611 116.
Did you know that you can report a side effect to a medicine to CARM (Centre for Adverse Reactions Monitoring)? Report a side effect to a product(external link)

Medsafe Consumer Information Sheet Trisul(external link)



5 questions to ask about your medications(external link) Health Quality and Safety Commission, NZ, 2019 English(external link), te reo Māori(external link)


Co-trimoxazole paediatric dose calculator


  1. Trimethoprim + sulfamethoxazole(external link) New Zealand Formulary

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Credits: Sandra Ponen, Pharmacist, Healthify He Puna Waiora. Healthify is brought to you by Health Navigator Charitable Trust.

Reviewed by: Angela Lambie, Pharmacist, Auckland

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