Pregnancy, breastfeeding and fertility while taking trimethoprim

Trimethorprim and pregnancy

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).

Trimethoprim and breastfeeding

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.

Trimethoprim and fertility

There's no evidence to suggest that taking trimethoprim affects fertility in either men or women.

But if you're trying to get pregnant and you are taking trimethoprim every day, talk to your doctor. This medicine can lower folic acid levels and is not usually recommended in early pregnancy. Your doctor may recommend changing to another antibiotic, or they may also prescribe high dose folic acid (5mg per day).