1. About cefalexin

Cefalexin is an antibiotic. It belongs to a group of antibiotics called cephalosporins. It’s used to treat bacterial infections, such as pneumonia and other chest infections, skin infections and urinary tract infections (UTIs).

Cefalexin is only available on prescription. It comes as capsules, tablets or as a liquid for children and people who find it difficult to swallow capsules or tablets.

2. Key facts

  • You’ll usually start to feel better in a few days, depending on the type of infection you have.
  • The most common side effects of cefalexin are feeling sick (nausea) and diarrhoea.
  • You can drink alcohol while taking cefalexin.
  • It’s important to keep taking cefalexin until you’ve completed the course, even if you feel better.

3. Who can and cannot take cefalexin

  • Cefalexin can be taken by most adults and children.
  • Cefalexin is not suitable for some people. To make sure cefalexin is safe for you, tell your doctor if you have:
  • had an allergic reaction to cefalexin or any other medicine in the past
  • kidney problems
  • ever had a severe skin rash or skin peeling, blistering and/or mouth sores after taking antibiotics
  • had severe or bloody diarrhoea when you’ve taken antibiotics before

4. Sut a phryd i'w gymryd

Always follow the advice of your doctor and the instructions that come with your medicine.


  • The dose of cefalexin can vary but for most infections you will take 500mg, two or three times a day.
  • The dose may be higher for severe infections and lower for children.
  • Try to space the doses evenly throughout the day. If you take it 3 times a day, this could be first thing in the morning, mid-afternoon and at bedtime.


Keep taking this medicine until you’ve completed the course, even if you feel better. If you stop your treatment early, the infection could come back.

How to take it

Cefalexin can be taken with or without food.

Capsules or tablets – swallow whole with a drink of water. Do not chew or break them.

Liquid – if you or your child are taking cefalexin as a liquid, it will usually be made up for you by a pharmacist. The medicine will come with a plastic syringe or medicine spoon to help you measure the right dose. If you do not have one, ask a pharmacist for one. Do not use a kitchen teaspoon as it will not give the right amount.

What if I forget to take it?

If you forget to take a dose, take it as soon as you remember, unless it’s nearly time for your next dose. In this case, skip the missed dose and take your next dose at the usual time. Try to leave a gap of at least 4 hours between doses.

Never take 2 doses at the same time. Never take an extra dose to make up for a forgotten one.

If you forget doses often, it may help to set an alarm to remind you. You could also ask a pharmacist for advice on other ways to remember your medicines.

What if I take too much?

  • Accidentally taking 1 extra dose of cefalexin is unlikely to harm you or your child.
  • Speak to a pharmacist or doctor if you’re worried or you take 2 extra doses or more.

5. Side effects

  • Like all medicines, cefalexin can cause side effects, although not everyone gets them.
  • Fewer than 1 in 100 people may have an allergic reaction to cefalexin. In most cases, the allergic reaction is mild.

Non-urgent advice: Contact your doctor if:

you get a raised, itchy skin rash

Common side effects

  • These common side effects happen in around 1 in 10 people.
  • Keep taking the medicine, but talk to your doctor or pharmacist if these side effects bother you or do not go away:
  • feeling sick (nausea)
  • diarrhoea
  • stomach pain

Serious side effects

  • Serious side effects are rare and happen in less than 1 in 1,000 people.
  • Call your doctor immediately if you get:
  • severe diarrhoea that lasts for more than 4 days or contains blood or mucus
  • pale poo and dark pee, yellowing of your skin or whites of your eyes – this may be a sign of liver problems
  • bruised skin

Serious allergic reaction

In rare cases, cefalexin can cause a serious allergic reaction (anaphylaxis).

Immediate action required: Call 999 or go to A&E if:

  • you get a skin rash that may include itchy, red, swollen, blistered or peeling skin or fever
  • you’re wheezing
  • you get tightness in your chest or throat
  • you have trouble breathing or talking
  • your mouth, face, lips, tongue or throat start swelling
  • You could be having a serious allergic reaction and may need immediate treatment in hospital.
  • These are not all the side effects of cefalexin. For a full list see the leaflet inside your medicine packet.


  • You can report any suspected side effect to the UK safety scheme.

6. How to cope with side effects

Beth i'w wneud am:

  • feeling sick – eat simple meals and do not eat rich or spicy food while you’re taking this medicine. It might help to take your cefalexin after a meal or snack.
  • diarrhoea – drink lots of fluids, such as water or squash, to avoid dehydration. Signs of dehydration include 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.
  • stomach pain – putting a heat pad or covered hot water bottle on your stomach may help stomach pain.

7. Pregnancy and breastfeeding

It’s usually safe to take cefalexin during pregnancy and while breastfeeding.

Read about how cephalosporin antibiotics like cefalexin can affect you and your baby on the Best Use of Medicines in Pregnancy (BUMPS) website.


For safety, tell your doctor if you’re trying to get pregnant, are already pregnant or if you’re breastfeeding.

8. Cautions with other medicines

There are some medicines that do not mix well with cefalexin.

Tell your doctor if you’re taking any of these medicines before you start taking cefalexin:

  • probenecid (a medicine used to treat gout)
  • metformin (a medicine used to treat diabetes)
  • medicines that make you pee more (diuretics) including furosemide
  • other antibiotics

Mixing cefalexin with herbal remedies and supplements

Do not take cefalexin at the same time as zinc supplements or anything with zinc in it. This is important because zinc may reduce the amount of cefalexin in your body, meaning the medicine cannot work as it’s meant to.

If you do take supplements with zinc in them, make sure there is a gap of at least 3 hours before and after you take your cefalexin.


For safety, tell your doctor or a pharmacist if you’re taking any other medicines, including herbal remedies, vitamins or supplements.

9. Common questions

  1. Sut mae cefalexin yn gweithio?

    Cefalexin is from a group of medicines called cephalosporin antibiotics. It works by killing the bacteria that causes the infection.

    Cefalexin can treat a wide range of bacteria so it works well for a variety of infections, such as chest, skin or urinary tract infections (UTIs).

  2. Pa mor hir mae'n ei gymryd i weithio?

    For most infections, you’ll start to feel better in a few days, but this depends on the type of infection you have.
    It is important that you take the full course your doctor has advised, even if you feel better. It will stop the infection coming back.

  3. Beth os na fyddaf yn gwella?

    Dywedwch wrth eich meddyg os na fyddwch chi'n dechrau teimlo'n well ar ôl cymryd cefalexin am 2 i 3 diwrnod, neu os ydych chi'n teimlo'n waeth ar unrhyw adeg.

  4. Pa mor hir y byddaf yn ei gymryd?

    Your doctor will tell you how long to take cefalexin for, as this can vary depending on the type of infection you have. Cefalexin is generally used for a short time to treat an infection. It can also be used long term to prevent infections which keep coming back.

    For some types of infection, you may need to take cefalexin for at least 10 days.

  5. Beth yw ymwrthedd i wrthfiotigau?

    If you need to take antibiotics like cefalexin often, they can become less effective as the bacteria gets used to the medicine. This is called antibiotic resistance. If your symptoms start to get worse again, tell your doctor or a pharmacist.

    If your symptoms do not improve at all after a few days, or they start to get worse again, tell your doctor or a pharmacist.

    Do not stop taking your medicine early, even if you feel better, as this makes it more likely that the infection will come back and the bacteria will be resistant to cefalexin.

  6. Beth fydd yn digwydd os byddaf yn rhoi'r gorau i'w gymryd?

    Carry on taking cefalexin until you’ve completed the course, even if you feel better. Do not stop taking it early, as there’s a risk the infection could come back. It also gives any remaining bacteria a chance to change or adapt, which means the antibiotic could stop working. This is known as antibiotic resistance.

  7. Sut mae'n wahanol i wrthfiotigau eraill?

    Cefalexin belongs to a group of antibiotics called cephalosporins. This group also includes other antibiotics such as cefradine, cefuroxime and ceftazidime.

    Different antibiotics are used to treat different infections. Your doctor will choose the antibiotic based on which bacteria they think is causing your infection.

    Cefalexin can treat a wide range of bacteria so it works well for a variety of infections, such as chest, skin or urinary tract infections (UTIs). Cefalexin can only be given as capsules, tablets or a liquid, but some other antibiotics can be given as injections.

  8. A allaf yfed alcohol ag ef?

    -Ydw, gallwch barhau i yfed alcohol gyda cefalexin.
    -A oes bwydydd a diodydd y dylwn eu hosgoi?
    -Na, gallwch chi fwyta ac yfed fel arfer wrth gymryd cefalexin.

  9. A fydd yn effeithio ar fy atal cenhedlu?

    Cefalexin does not affect contraceptive pills working, including the combined pill and emergency contraception.

    However, if cefalexin makes you vomit or have severe diarrhoea for more than 24 hours, your contraceptive pills may not protect you from pregnancy. Look on the pill packet to find out what to do. Read more about what to do if you’re on the pill and you’re being sick or have diarrhoea.

  10. A fydd yn effeithio ar fy ffrwythlondeb?

    There is no firm evidence to suggest cefalexin will affect fertility in men or women. However, speak to a pharmacist or your doctor before taking it if you’re trying to get pregnant.

  11. A allaf yrru neu reidio beic?

    Oes, ni fydd cefalexin yn effeithio arnoch chi'n gallu gyrru neu reidio beic.

Related conditions

  • Chest infection
  • Ear infections
  • Urinary tract infections (UTIs)
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