Trimethoprim

Trimethoprim is not suitable for some people. For example, if you've ever had kidney problems or been allergic to a medicine, check with a doctor.

Trimethoprim comes as tablets or a liquid that you usually take twice a day. Follow the instructions that come with your medicine.

Common side effects of trimethoprim include itching and a mild rash. More serious side effects can happen in rare cases.

Trimethorprim can be taken in pregnancy but is not usually recommended before 12 weeks. Check with a pharmacist or doctor first.

Most adults and children can take trimethoprim.

Trimethoprim is not suitable for some people. To make sure it's safe for you, tell your doctor before starting to take trimethoprim if you:

• have ever had an allergic reaction to trimethoprim or any other medicine
• have liver or kidney problems
• have iron deficiency anaemia or low amounts of folic acid (vitamin B12 or folate deficiency anaemia) in your blood
• have porphyria (a rare inherited blood disorder) or any other blood disorder
• are trying to get pregnant or are already pregnant

Trimethoprim tablets contain 100mg or 200mg. The liquid contains 50mg in 5ml.

To treat urinary tract infections (UTIs) in adults, the usual dose is 200mg twice a day.

To prevent infections, the usual adult dose is 100mg once a day at night.

If you know what causes your cystitis, take one single dose of 200mg after you’ve been exposed to the trigger.

To treat acne, the usual adult dose is 300mg twice a day. This dose might be reduced over time.

The dose of trimethoprim you need to take depends on your condition, your age, and how well your kidneys work.

Doses are usually lower for children, older people and those with kidney problems.

Stopping trimethoprim

Carry on taking this medicine until you finish the course, even if you feel better. If you stop your treatment early, your problem could come back.

How to take trimethoprim

Trimethoprim tablets

If you're taking trimethoprim to treat an infection, you'll usually take it twice a day, once in the morning and once in the evening.

If you're taking trimethoprim once a day to prevent an infection, take it at bedtime.

If you know what triggers your cystitis and want to stop an infection before it starts, take trimethoprim as a single dose after being exposed to the trigger.

You can take trimethoprim with or without food.

Swallow trimethoprim tablets whole with a drink of water. Do not chew or break them.

You can take it as a liquid if you find it difficult to swallow tablets.

Trimethoprim liquid

If you're taking trimethoprim as a liquid, shake the bottle gently before measuring out the right amount using a medicine spoon or oral syringe. If you do not have an oral syringe or medicine spoon, ask your pharmacist for one. Do not use a kitchen teaspoon as it will not measure the right amount.

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:

It may help to use an emollient cream or gentle, fragrance-free moisturising cream, or take an antihistamine, which you can buy from a pharmacy. Check with a pharmacist to see what may be suitable for you.

Try taking trimethoprim with or after food to see if that helps your symptoms. It may also help if you stick to simple meals and avoid rich or spicy food while you're taking this medicine.

If you're being sick, try small frequent sips of water to avoid dehydration. Signs of dehydration include peeing less than usual or having dark, strong-smelling pee.

If you take the combined contraceptive pill or progestogen-only pill and you're being sick, your contraception may not protect you from pregnancy. Check the pill packet to find out what to do.

Drink lots of water or squash to avoid dehydration. Speak to a doctor or pharmacist if you have signs of dehydration such as peeing less than usual or having dark, strong-smelling pee.

Do not take any other medicines to treat diarrhoea without speaking to a pharmacist or doctor.

If you take the combined contraceptive pill or progestogen-only pill and you have severe, watery diarrhoea or any diarrhoea that lasts for more than 24 hours, your contraception may not protect you from pregnancy. Check the pill packet to find out what to do.

Trimethoprim can sometimes cause the infection, thrush. Drying properly after washing, wearing cotton underwear and avoiding sex until it's cleared up can help.

Make sure you rest and drink plenty of fluids. It's best not to drink too much alcohol. Everyday painkillers, such as paracetamol and ibuprofen, are safe to take with trimethoprim. Speak to your doctor if these do not help or the headaches are severe and do not go away.

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.

Trimethoprim can be taken in pregnancy, but it's not usually recommended in the first 12 weeks. This is because it may lower your levels of folic acid, which is important in the early stages of your baby's development.

Sometimes trimethoprim is the only suitable antibiotic to treat an infection. In this case, the benefit of taking it is likely to outweigh the risk of harm. Your doctor will help you decide whether taking it is right for you.

If you're trying to get pregnant or you're in the first 12 weeks of pregnancy and you need to take trimethoprim, a doctor will usually prescribe a higher dose folic acid (5mg per day).

You may be able to take trimethoprim while breastfeeding but check with a pharmacist or doctor first.

Trimethoprim passes into breast milk in small amounts and is unlikely to cause side effects in your baby if you take it for a short time.

It's rare for breastfed babies to get side effects from medicines you're taking, but speak to a healthcare professional or call 111 if you have any concerns about your baby.

Some medicines affect the way trimethoprim works and increase the chances of you having side effects.

Check with a pharmacist or your doctor if you're taking any other medicines, including:

• rifampicin, an antibiotic
• warfarin or acenocoumarol (Sinthrome), medicines to treat or help prevent blood clots (anticoagulants)
• digoxin, a heart medicine
• phenytoin, an epilepsy medicine
• replaglinide or pioglitazone, diabetes medicines
• methotrexate, an immune system medicine, also used to treat some types of cancer

These are not all the medicines that may cause problems if you take them with trimethoprim. For a full list, see the leaflet inside your medicine packet.

Tell your doctor if you've recently had, or are due to have, an oral typhoid vaccine. Trimethoprim can make it less effective.