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Cefalexin for infection


Before you take cefalexin, make sure your doctor knows if you have ever had an allergic reaction to an antibiotic.

Space out your doses evenly over the day and complete the full course.

The most common side-effect is diarrhoea, which is usually mild and soon passes. If it becomes severe or lasts for more than 24 hours, you should speak with your doctor.

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About cefalexin

Type of medicine

A cephalosporin antibiotic

Used for

Treatment (and sometimes prevention) of infection

Also called

Cephalexin (in US); Keflex®

Available as

Capsules, tablets, and oral liquid medicine

Cefalexin is a broad-spectrum antibiotic, which means that it is active against a wide variety of germs (bacteria). It is used to treat bacterial infections such as urinary tract infections, skin infections, chest and throat infections, ear infections and dental infections. It is suitable for adults and children and can be taken during pregnancy. Some people who are allergic to penicillin antibiotics may not be able to take cefalexin, so make sure your doctor knows if you have ever had an allergic reaction to any other antibiotic.

Cefalexin treats an infection by killing the bacteria that are causing it.

Before taking cefalexin

Some medicines are not suitable for people with certain conditions, and sometimes a medicine may only be used if extra care is taken. For these reasons, before you (or your child, if appropriate) start taking cefalexin it is important that your doctor knows:

  • If you have ever had an allergic reaction to a medicine. It is particularly important that you tell your doctor if you have had a bad reaction to a penicillin or cephalosporin antibiotic.

  • If you have any problems with the way your kidneys work.

  • If you are pregnant, trying for a baby or breastfeeding. Although cefalexin is not known to be harmful to babies, it is still important that you tell your doctor if you are expecting or breastfeeding a baby.

  • If you are taking or using any other medicines. This includes any medicines you are taking which are available to buy without a prescription, as well as herbal and complementary medicines.

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How to take cefalexin

  • Before you start taking cefalexin, read the manufacturer's printed information leaflet from inside the pack. It will give you more information about the antibiotic and will provide you with a full list of side-effects which you could experience from taking it.

  • As a guide, it is usual to take 2-4 doses of cefalexin daily to treat an infection. Your doctor will tell you what dose is right for you (or your child) and the directions for taking it will be printed on the label of the pack to remind you about what the doctor said to you. If you have been given cefalexin liquid medicine to give to your child, please read the directions carefully to make sure that you give the correct amount. Your doctor will tell you how long your course of treatment will last - this is commonly about 5-7 days, although it could be for longer or shorter periods of time than this. It is important that you take cefalexin exactly as your doctor tells you to.

  • If you have been prescribed cefalexin to prevent a urinary tract infection from recurring, you are likely to be asked to take just one dose a day. Please take it in the evening. A course of treatment such as this can last for some time.

  • Cefalexin can be taken either before or after food, although it may start to work a little sooner if it is taken before food.

  • Space the doses evenly throughout the day. Keep taking this medicine until the course is finished unless you are told to stop. It is important to take the full course (even if you feel your infection has cleared up) in order to prevent the infection from coming back.

  • If you forget to take a dose, take one as soon as you remember. Try to take the correct number of doses each day but do not take two doses at the same time to make up for a missed dose.

Getting the most from your treatment

  • If you are having an operation or any other medical treatment, tell the person carrying out the treatment that you are taking an antibiotic. This is because cefalexin can interfere with the results of some medical tests.

  • Some people develop redness and itching in the mouth or vagina (thrush) after taking a course of antibiotics. If after taking cefalexin you think you could have thrush, please speak with your doctor or pharmacist for advice.

  • If you are taking the contraceptive 'pill' at the same time as an antibiotic, the effectiveness of the 'pill' can be reduced if you have a bout of being sick (vomiting) or diarrhoea which lasts for more than 24 hours. If this should happen, ask your doctor or pharmacist for advice about what additional contraceptive precautions to use. There is no need to use additional precautions for any bouts of sickness or diarrhoea which last for less than 24 hours.

  • Antibiotics like cefalexin can stop the oral typhoid vaccine from working properly. If you are due to have any vaccinations, please make sure the person treating you knows that you are taking this antibiotic.

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Can cefalexin cause problems?

Along with their useful effects, most medicines can cause unwanted side-effects although not everyone experiences them. The table below contains some of the ones associated with cefalexin. You will find a full list in the manufacturer's information leaflet supplied with the medicine. The unwanted effects often improve as your body adjusts to the new medicine, but speak with your doctor or pharmacist if any of the following continue or become troublesome.

Cefalexin side-effects

What can I do if I experience this?


Drink plenty of water to replace the lost fluids. If the diarrhoea continues for longer than 24 hours, becomes severe, or contains blood, please let your doctor know


Indigestion, stomach ache, feeling sick (nausea)

Stick to simple foods. If you are not already doing so, try taking your doses after meals


Speak with your doctor or pharmacist for advice

Important: if you develop an itchy rash, swollen face or mouth, or have difficulty breathing, these can be signs that you are allergic to the antibiotic. Do not take any more doses, and speak with your doctor or go to your local accident and emergency department straightaway.

If you experience any other symptoms which you think may be due to the antibiotic, please speak with your doctor or pharmacist for further advice.

How to store cefalexin

  • Keep all medicines out of the reach and sight of children.

  • Store tablets and capsules in a cool, dry place, away from direct heat and light.

  • If you have been given liquid medicine, store it in a refrigerator. It will have been made up freshly by the pharmacy and lasts for 14 days, so please remember to check the expiry date, and do not use it after this date.

Important information about all medicines

Important information about all medicines

Do not take more than the prescribed dose. If you suspect that you or someone else might have taken an overdose of this medicine, go to the accident and emergency department of your local hospital. Take the container with you, even if it is empty.

This medicine is for you. Never give it to other people even if their condition appears to be the same as yours.

If you buy any medicines, check with a pharmacist that they are safe to take with your other medicines.

If you are having an operation or any dental treatment, tell the person carrying out the treatment which medicines you are taking.

Do not keep out-of-date or unwanted medicines. Take them to your local pharmacy which will dispose of them for you.

If you have any questions about this medicine ask your pharmacist.

Report side effects to a medicine or vaccine

If you experience side effects, you can report them online through the Yellow Card website.

Further reading and references

Article History

The information on this page is written and peer reviewed by qualified clinicians.

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