Cephalexin: A Guide to the Cephalosporin Antibiotic

What cephalexin is

Cephalexin is an antibiotic from the cephalosporin family, which is related to penicillins. It works by weakening the cell walls of bacteria so they cannot survive. It is a prescription-only medicine across the UK and EU and is commonly used for a range of everyday bacterial infections.

Because cephalosporins are chemically related to penicillins, people with a penicillin allergy should always tell their prescriber, as there can sometimes be cross-reactivity.

What it is used for

Doctors may prescribe cephalexin for infections such as:

• Some skin and soft-tissue infections
• Certain urinary tract infections
• Some respiratory and throat infections
• Particular bone and ear infections

Cephalexin treats bacterial infections only and has no effect on viral illnesses like colds or flu. Using antibiotics only when needed helps limit antibiotic resistance explained. To understand more, read bacterial infections explained.

How to take it safely

Always follow your prescriber's instructions and the patient information leaflet. General principles include:

• Finish the whole course. Stopping early because you feel better can let the infection rebound and encourages resistant bacteria.
• Space doses evenly through the day to keep a steady level in your body.
• Take with or without food as directed; taking it with food can ease stomach upset.
• Tell your prescriber about any allergies, particularly to penicillin or other antibiotics, and about other medicines you take.

If you miss a dose, take it as soon as you remember unless it is nearly time for the next one. Do not take a double dose.

Possible side effects

Most people tolerate cephalexin well. Common side effects include nausea, stomach upset and diarrhoea, which are usually mild. As with many antibiotics, disturbing the gut's natural bacteria can occasionally lead to thrush or more troublesome diarrhoea.

Seek urgent medical help if you notice signs of a serious allergic reaction, such as a rash, swelling of the lips, face or throat, or difficulty breathing. Severe, watery or bloody diarrhoea during or after treatment should also be reported promptly.

Allergy, alcohol and contraception

If you have ever reacted to a penicillin or cephalosporin antibiotic, this is essential information for your prescriber. Cephalexin does not have a dangerous interaction with alcohol, but moderation helps your body recover and limits stomach upset. As with other antibiotics, vomiting or severe diarrhoea can reduce absorption of the contraceptive pill, so use backup protection and ask your pharmacist if this occurs.

When to see a doctor

Contact your doctor if your symptoms fail to improve within a few days, worsen, or return after the course. Always seek advice before starting if you are pregnant, breastfeeding, have kidney problems, or take other regular medicines.

You can explore our full antibiotics range, compare it with the Amoxicillin guide, or shop all for general wellbeing products. Used appropriately and completed in full, cephalexin is a dependable antibiotic for many common bacterial infections.

General information only — not medical advice. Always read the patient information leaflet and consult a doctor or pharmacist before starting any medication.