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  • Before taking cefalexin, make sure your doctor knows if you have ever had an allergic reaction to any other antibiotic.
  • Take cefalexin at regular intervals and complete the course your doctor has prescribed for you.
  • The most common side-effect is diarrhoea. If this is severe or lasts for more than 24 hours, speak with your doctor.
Type of medicineCephalosporin antibiotic
Used forInfections such as urinary tract, chest, dental and ear infections
Also calledCeporex®, Keflex®
Available asCapsules, tablets, and oral liquid

Cefalexin is a broad-spectrum antibiotic, which means it is active against a wide variety of bacteria. It treats infections by killing or stopping the growth of the bacteria that cause them.

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 start taking cefalexin it is important that your doctor or pharmacist knows:

  • If you are pregnant, trying for a baby or breast-feeding. Cefalexin is not known to be harmful to unborn babies; however it is important that your doctor knows if you are expecting a baby.
  • If you have kidney problems.
  • If you have ever had an allergic reaction to this or to any other medicine. It is particularly important that you tell your doctor if you are allergic to any other antibiotics (such as penicillin).
  • If you are taking or using any other medicines. This includes any medicines you are taking which are available to buy without a prescription, such as herbal and complementary medicines.
  • If you have porphyria (this is a rare inherited blood disorder).
  • Before you start this antibiotic, read the manufacturer's printed information leaflet from inside your pack. The leaflet will give you more information about the specific brand of cefalexin you have been given, and a full list of side-effects which you may experience from taking it.
  • As a guide, it is usual to take 2-4 doses of cefalexin daily for 5-7 days; however, your doctor will tell you what dose is right for you and your dose will also be on the label of the pack to remind you. Your course of treatment may be for longer or shorter periods of time than this, so it is important that you take cefalexin exactly as your doctor has told you. If you are taking cefalexin to prevent urinary tract infections from recurring, you are likely to be prescribed just one dose daily, which you should take each evening. If you have been given cefalexin liquid medicine to give to your child, read the directions carefully to make sure you give the correct amount.
  • You can take cefalexin before, during or after your meals.
  • 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 unless it is nearly time for your next dose. If it is almost time to take your next dose, skip the missed dose and take your next dose when it is due. Do not take two doses together to make up for a forgotten dose.
  • Some people develop thrush (redness and itching in the mouth or vagina) after taking a course of antibiotics. If you think you have thrush speak with your doctor or pharmacist for advice.
  • If you are using oral combined hormonal contraception (the 'pill'), additional contraceptive precautions such as condoms are not required during a course of this antibiotic unless you are sick or have diarrhoea. If you need further advice about this, speak with your doctor or pharmacist.
  • If you are having an operation or dental treatment, tell the person carrying out the treatment that you are taking an antibiotic. This is because cefalexin may interfere with the results of some medical tests.
  • Cefalexin may stop the oral typhoid vaccine from working. If you are having any vaccinations, make sure the person treating you knows that you are taking this medicine.
  • If you buy any medicines, check with a pharmacist that they are suitable for you to take with cefalexin.

Along with their useful effects, most medicines can cause unwanted side-effects although not everyone experiences them. These usually improve as your body adjusts to the new medicine, but speak with your doctor or pharmacist if any of the following side-effects continue or become troublesome.

Cefalexin side-effectsWhat can I do if I experience this?
DiarrhoeaDrink plenty of water to replace lost fluids.
If the diarrhoea is severe or lasts for more than 24 hours,
you should contact your doctor for further advice
Indigestion, stomach ache, feeling sickStick to simple foods. Try taking your doses after meals
ThrushSpeak with your doctor or pharmacist for advice

Important: if you experience any of the following symptoms, contact your doctor for advice straightaway:

  • A severe skin rash.
  • Jaundice (yellowing of your skin or the whites of your eyes), fever, and pain in your joints.
  • Swelling of your tongue, mouth, or face.
  • Severe diarrhoea.

If you experience any other symptoms which you think may be due to this medicine, speak with your doctor or pharmacist.

  • Keep all medicines out of the reach and sight of children.
  • Store cefalexin tablets and capsules in a cool, dry place, away from direct heat and light.
  • Store cefalexin liquid medicine in a refrigerator and do not use it after the expiry date shown on the label.

  • Never 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.
  • Never 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.

Further reading & references

Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.

Original Author:
Helen Allen
Current Version:
Peer Reviewer:
Dr Adrian Bonsall
Document ID:
3414 (v25)
Last Checked:
Next Review:
The Information Standard - certified member
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