Sounds like 'tri-meth-o-prim'

Easy-to-read medicine information about trimethoprim – what it is, how to take trimethoprim safely and possible side effects.

Type of medicine Also called
  • Antibiotic (to treat infection)
  • TMP Tablet®

What is trimethoprim?

Trimethoprim is an antibiotic that is used to treat and prevent urine infections. It works by killing or stopping the growth of bacteria (bugs) and getting rid of the infection. In New Zealand, trimethoprim is available as tablets (300 mg).

Can I get trimethoprim from my pharmacy without a prescription?

Many pharmacists are now able to sell trimethoprim for the treatment of UTIs. This is available without a prescription to women aged between 16 to 65 years, who are not pregnant and do not have any other complicating factors.

Only pharmacists who have completed additional training can supply trimethoprim. They will need to ask you questions to make sure it is the best option for you and will need to record your name and address. 


  • The usual dose for adults with an infection is 1 tablet (300mg), each night. Your doctor or pharmacist will advise you how long to take trimethoprim for (usually 3 to 7 days).
  • The dose to prevent infection is half a tablet (150mg) at night. If you have frequent urine infections, you will have to take trimethoprim each night for a few months to prevent recurrent infections.
  • Always take your trimethoprim exactly as your doctor has told you. The pharmacy label on your medicine will tell you how much trimethoprim to take, how often to take it, and any special instructions.

How to take trimethoprim

  • You can take trimethoprim with or without food. If you get stomach upset, try taking it with food.
  • It is important to take the whole course of antibiotics for the number of days your doctor has told you to.  
  • If you forget to take trimethoprim, take it as soon as you remember. But, if it is nearly time for your next dose, just take the next dose at the right time. Do not take double the dose.

Precautions – before starting trimethoprim

  • Are you pregnant, planning a pregnancy or breastfeeding?
  • Do you have problems with the way your kidneys work?
  • Do you have allergies to antibiotics?
  • Are taking any other medicines? This includes any medicines you are taking which you can buy without a prescription, as well as herbal and complementary medicines.

If so, it’s important that you tell your doctor or pharmacist before you start trimethoprim. Sometimes a medicine isn’t suitable for a person with certain conditions, or it can only be used with extra care.

Side effects

Like all medicines, trimethoprim can cause side effects, although not everyone gets them. Often side effects improve as your body adjusts to the new medicine

Side effects What should I do?
  • Headache
  • Feeling sick or nausea
  • Decreased appetite
  • Difficulty sleeping
  • These are quite common when you first start taking trimethoprim and usually go away with time.
  • Try taking trimethoprim with food.
  • Tell your doctor if troublesome.
  • Signs of problems with your liver such as yellowing of the skin or eyes, pain in the abdomen
  • Tell your doctor immediately or ring HealthLine 0800 611 116
  • Sore throat or mouth, fever, rash, bruising or bleeding
  • Tell your doctor immediately or ring HealthLine 0800 611 116
  • Signs of an allergic reaction such as skin rashes, redness, itching, blisters on the skin
  • Tell your doctor immediately or ring HealthLine 0800 611 116


Trimethoprim may interact with some medicines and herbal supplements so check with your doctor or pharmacist before starting trimethoprim or before starting any new medicines.

Learn More

Medsafe Consumer Information Sheet   TMP Tablet

New Zealand Formulary Patient Information: trimethoprim


  1. Trimethoprim New Zealand Formulary
Credits: Sandra Ponen, Pharmacist. Reviewed By: Angela Lambie, Pharmacist, Auckland Last reviewed: 14 Feb 2019