Side Effects Of Trimethoprim

Like all medicines, trimethoprim can cause side effects in some people, but many people have no side effects or only minor ones.

Common side effects of trimethoprim

These common side effects of trimethoprim happen to more than 1 in 100 people. There are things you can do to help cope with them:

Speak to a doctor or pharmacist if the advice on how to cope does not help and a side effect is still bothering you or does not go away.

Serious side effects

Most serious side effects are rare and happen in less than 1 in 1,000 people.

Call a doctor or call 111 straight away if:

• you have diarrhoea that contains blood or mucus, or severe diarrhoea
• you have sudden, severe pain in your stomach, and may be feeling or being sick (nausea and vomiting) - these can be signs of pancreatitis
• the whites of your eyes turn yellow, or your skin turns yellow, although this may be less obvious on brown or black skin - this can be a sign of liver problems
• you get bruising or bleeding you cannot explain (including nosebleeds), a sore throat, mouth ulcers, a high temperature, or you feel tired or generally unwell - these can be signs of a problem with your blood
• you have serious skin reactions or rashes, including, round red patches, peeling, blisters, skin ulcers, or swelling of the skin that look like burns

Call 999 or go to A&E now if:

Do not drive to A&E. Ask someone to drive you or call 999 and ask for an ambulance.

Bring all the medicines you take with you.

Serious allergic reaction

In rare cases, trimethoprim may cause a serious allergic reaction (anaphylaxis).

Call 999 now if:

• your lips, mouth, throat or tongue suddenly become swollen
• you're breathing very fast or struggling to breathe (you may become very wheezy or feel like you're choking or gasping for air)
• your throat feels tight or you're struggling to swallow
• your skin, tongue or lips turn blue, grey or pale (if you have black or brown skin, this may be easier to see on the palms of your hands or soles of your feet)
• you suddenly become very confused, drowsy or dizzy
• someone faints and cannot be woken up
• a child is limp, floppy or not responding like they normally do (their head may fall to the side, backwards or forwards, or they may find it difficult to lift their head or focus on your face)

You or the person who's unwell may also have a rash that's swollen, raised, itchy, blistered or peeling.

These can be signs of a serious allergic reaction and may need immediate treatment in hospital.

Other side effects

These are not all the side effects of trimethoprim. For a full list, see the leaflet inside your medicine packet.

Reporting side effects

You can report any suspected side effect using the Yellow Card safety scheme.

Visit the Yellow Card website for more information about reporting side effects.

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