Cefalexin

What is cefalexin?

Cefalexin – sometimes spelled and known as cephalexin – is an antibiotic medicine. It belongs to a group of antibiotics called cephalosporins, commonly used to treat bacterial infections by stopping the growth of bacteria[1]. 

What is cefalexin used for?

Cefalexin can be prescribed for a number of different infections, including[1]: 

• Urinary tract infections (UTIs) 

• Chest infections such as pneumonia 

• Skin infections 

• Ear infections 

• Bone infections 

• Dental infections 

It is effective against a wide range of bacteria. However, cefalexin will not treat viral infections such as colds or flu[1].

How does cefalexin work?

Cefalexin fundamentally works by damaging the cell wall of harmful bacteria. This then causes the bacteria to rupture and die, stopping the infection from spreading. Over time, this allows the immune system to clear the remaining bacteria from the body and for the patient to make a recovery from the infection[1]. 

Who can take cefalexin?

Most adults and children can take cefalexin. However, it may not be suitable for people with certain conditions or taking other medications. These include those who have had an allergic reaction to cefalexin or other antibiotics, especially penicillin or other cephalosporins, or who have kidney issues. You should also let your doctor know if you have ever had severe or bloody diarrhoea or a severe skin rash or skin peeling, blistering or mouth sores after taking antibiotics[1]. 

Please tell your doctor or pharmacist about any conditions you may have before you start treatment and always follow the instructions in the Patient Information Leaflet[2]. 

How do you take cefalexin?

When you take cefalexin, you can swallow your tablets or capsules whole with water,with or without food. Taking it with food may help reduce stomach upset and prevent side effects. Do not chew or break them. If you have been prescribed cefalexin in liquid form, shake it well before use and measure it with a dosing spoon or syringe for best accuracy. Follow your healthcare provider’s instructions carefully no matter the type or dose you’ve been prescribed[1]. 

What is the typical dosage of cefalexin?

The usual dosage of cefalexin depends on the type and severity of the infection you’re experiencing. It may also vary due to your age and kidney function. Typically, adults are prescribed 500mg every 6 to 12 hours. Children are given a dose based on their weight and age, usually as a liquid. Please follow the dosage on your prescription label or as advised by your doctor[1]. 

Can you stop taking cefalexin suddenly?

No, you should not stop taking cefalexin suddenly. Instead, you should complete the full course – even if you feel better – as stopping early can cause the infection to return and may lead to antibiotic resistance[1]. 

What should you do if you take too much cefalexin?

Taking 1 extra dose of cefalexin is unlikely to harm you or your child. However, taking excessive amounts of cefalexin can cause symptoms such as nausea, vomiting, diarrhoea, or stomach pains. These can potentially be serious. If you or someone else takes too much, call 111 or get medical help immediately[1]. 

What should you do if you forget a dose of cefalexin?

If you forget a dose of cefalexin shortly after it was due, you can take the dose as normal. If the next dose is due soon, wait and take that one then continue as normal. Do not take a double dose to make up for missing one. Try and leave a gap of at least 4 hours between doses[1]. However, for treatment to be effective it is important to try and remember every dose. If you find you are frequently forgetting to take your medication, speak to your prescriber. 

What medicines should you avoid while taking cefalexin?

Cefalexin can interact with other medicines. For that reason, you should use caution if you are taking any of the following[1]: 

• Probenecid, sometimes used to treat gout 

• Warfarin, a blood thinner 

• Live vaccines, such as the typhoid vaccine 

• Other antibiotics  

• Zinc supplements 

Always inform your doctor or pharmacist about all medications and supplements you take before you start a new medicine, and follow the instructions in the Patient Information Leaflet[2]. 

What are the side effects of cefalexin?

Common side effects of cefalexin are usually mild. They can include diarrhoea, nausea, stomach pain, and a headache. More serious side effects include[1]: 

• Severe allergic reactions, including rash, swelling, or difficulty breathing 

• Severe diarrhoea, which may indicate a C. difficile infection 

• Yellowing of the skin or eyes, which may suggest liver problems, as well as pale poo and dark pee

• Unexplained bruising

You should contact your GP if you experience any of these symptoms. In rare cases, the medicine may cause a serious allergic reaction (anaphylaxis). You should call 999 or visit A&E immediately if you believe this is happening[1].

If you experience any side effects, including those not listed, you are encouraged to report them via the Yellow Card Scheme or contact your doctor, pharmacist, or nurse. This information is intended as a summary for general awareness and does not replace professional medical advice.

The information provided in the side effects section is not a comprehensive list of all possible side effects associated with this medication. For a complete list of side effects, please refer to the Patient Information Leaflet (PIL) provided with your medication or consult your healthcare professional[2].

Frequently asked questions about cefalexin

Can I drink alcohol while taking cefalexin? 

Yes, it’s usually safe to drink alcohol, as it does not affect how cefalexin works. However, it may increase the likelihood of side effects such as stomach upset, so it’s a good idea to only drink in moderation[1]. 

Can I take cefalexin if I am pregnant or breastfeeding? 

Yes, cefalexin is usually considered safe during pregnancy and breastfeeding. However, you should still only take it if advised and prescribed by a doctor first[1]. 

How long does cefalexin take to work? 

When you start taking cefalexin, you may start to feel better after a few days. It’s important to finish the prescribed course, even if your symptoms improve, to ensure a full recovery[1]. 

Is cefalexin a strong antibiotic? 

When it comes to antibiotics, it is not about strength but choosing the correct antibiotic for the type of infection you have. There aren't “strong” and “weak” antibiotics in the sense of how they work. 

Cefalexin works well for many common infections which makes it a good choice when prescribed.  

However, some infections need different antibiotics because the bacteria involved might not respond to cefalexin. This doesn’t mean cefalexin is weak in this case, just that it’s not the right antibiotic for that infection. 

If your doctor has prescribed cefalexin, this is because it is the correct antibiotic for the infection you have[1].

For the official NHS guide to cefalexin, visit their website.