Easy-to-read medicine information about cefalexin – what it is, how to take cefalexin safely and possible side effects.

Type of medicine Also called
  • Antibiotic (to treat infections)
  • Cefalexin ABM®
  • Keflex®

What is cefalexin?

Cefalexin is an antibiotic used to treat infections caused by bacteria, such as infections of the urinary tract, skin or chest. It can also be used for dental infections or ear infections. It works by killing or stopping the growth of bacteria (bugs) and gets rid of the infection. Cefalexin does not work against infections caused by viruses. In New Zealand cefalexin is available as capsules and liquid.


  • The usual dose of cefalexin in adults is 250 mg 4 times a day, or 500 mg 2 or 3 times a day. Some people may need higher doses.
  • The dose for children will depend on their body weight. It is usually given 2, 3 or 4 times a day.
  • Your doctor will advise you how long to take cefalexin for (usually 5 to 7 days).
  • Always take your cefalexin exactly as your doctor has told you. The pharmacy label on your medicine will tell you how much cefalexin to take, how often to take it, and any special instructions.

 How to take cefalexin

  • Capsule: swallow your capsules with a glass of water.
  • Liquid: shake the medicine well. Measure the right amount using an oral syringe or medicine spoon. You can get these from your pharmacy. Do not use a kitchen spoon as it will not give you the right amount. Read more: tips on how to give medicines to babies and children.
  • Try to space your doses evenly throughout the day.  
    • Twice a day: this should be once in the morning and once in the evening. Ideally, these times are 10–12 hours apart, for example between 7am and 8am, and between 7pm and 8pm.
    • Three times each day: this should be once in the morning, once in the early afternoon and once in the evening. Ideally, these times are at least 6 hours apart, for example 8am, 2 pm and 8pm. 
    • Four times each day: this should be once in the morning, once around midday, once in the early afternoon and once in the evening. Ideally, these times are about 4 hours apart, for example 8am, midday, 4pm and 8pm.  
  • You can take cefalexin with or without food.
  • If you forget to take your dose at the correct time, take one as soon as you remember. Try to take the correct number of doses each day. Do not take two doses at the same time to make up for a forgotten dose.
  • It is important to take the whole course of antibiotics for the number of days your doctor has told you to. 
  • You should start to get better after taking cefalexin for a few days. If you do not feel better or get more unwell, contact your doctor.

Precautions – before starting cefalexin

  • Have you ever had an allergic reaction to a medicine, especially a penicillin antibiotic?
  • Do you suffer from collitis or severe diarrhoea?
  • Do you have problems with your kidneys?
  • Are you pregnant or breastfeeding?
  • Are taking any other medicines? This includes any medicines you are taking which you can buy without a prescription, as well as herbal and complementary medicines.

If so, it’s important that you tell your doctor or pharmacist before you start cefalexin. Sometimes a medicine isn’t suitable for a person with certain conditions, or it can only be used with extra care.

Precautions – while taking cefalexin

  • Store your cefalexin capsules in a cool, dry place, away from direct heat and light.
  • If you have been given liquid medicine, this will have been made up by the pharmacy and you may need to keep it in the fridge – check the instructions on the bottle. Make sure the medicine does not freeze.
  • If your child is sick (vomits) and it is less than 30 minutes after having a dose of cefalexin, give them the same dose again. But, if your child is sick (vomits) and it is more than 30 minutes after having a dose of cefalexin, you do not need to give them another dose. Wait until the next dose is due.
  • If you are taking the contraceptive pill, the effectiveness of the pill can be reduced if you are sick (vomiting) or have diarrhoea which lasts for more than 24 hours. If this happens, ask your doctor or pharmacist for advice about contraception over the next few days.

Possible side effects

Like all medicines, cefalexin can cause side effects, although not everyone gets them. Often side effects improve as your body gets used to the new medicine.

Side effects What should I do?
  • Feeling sick (nausea) or vomiting
  • Dizziness, headache
  • Try taking cefalexin with food.
  • Tell your doctor if troublesome
  • Diarrhoea (runny poos)
  • This may settle after a few days.
  • Tell your doctor if troublesome.
  • Vaginal itching, soreness or discharge (thrush)
  • Ask your doctor or pharmacist for advice.
  • Signs of allergic reaction such as skin rash, itching, swelling of the lips, face, and mouth or difficulty breathing
  • Tell your doctor immediately or ring HealthLine 0800 611 116


Cefalexin interacts with a few important medications or herbal supplements, so check with your doctor or pharmacist before starting cefalexin.

Learn more

For adults: cefalexin New Zealand Formulary Patient Information
For children: cefalexin New Zealand Formulary for Children


  1. Cefalexin New Zealand Formulary
  2. Antibiotics: choices for common infections BPAC, 2017
Credits: Sandra Ponen, pharmacist. Reviewed By: Angela Lambie, Pharmacist, Auckland Last reviewed: 06 Dec 2018