Trimethoprim

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 gets rid of the infection. In New Zealand trimethoprim is available as tablets (300 mg).

Dose

  • The usual dose for adults with an infection is 1 tablet (300 mg), once a day at night. 
  • The dose to prevent infection is half a tablet (150 mg) at night.
  • Your doctor will advise you how long to take trimethoprim for. The usual course of treatment is usually 3 to 7 days. The course will be for longer than this if you are taking trimethoprim 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. Do not stop taking it, even if you feel your infection has cleared up. 
  • 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 breast-feeding?
  • Do you have problems with the way your kidneys work?
  • 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.

Possible 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.
  • 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
  • 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

Interactions

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

References

  1. Trimethoprim New Zealand Formulary
Credits: Sandra Ponen, Pharmacist. Reviewed By: Dr Janine Bycroft, GP, Health Navigator NZ