BMA Concise Guide to Medicine & Drugs


Brand names Ceporex, Keflex

Used in the following combined preparations None


Drug group Cephalosporin antibiotic

Overdose danger rating Low

Dependence rating Low

Prescription needed Yes

Available as generic Yes


Cefalexin is a cephalosporin antibiotic that is prescribed for a variety of mild to moderate infections. It does not have such a wide range of uses as some other antibiotics, but it is helpful in treating respiratory tract infections, cystitis, ear infections and certain skin and soft tissue infections. In some cases it is prescribed as follow-up treatment for severe infections after a more powerful cephalosporin has been given by injection.

Diarrhoea is the most common adverse effect of cefalexin. Although this tends to be less severe than with other cephalosporins, the risk of the more dangerous Clostridium difficile diarrhoea is much higher for elderly patients taking cefalexin (or any other cephalosporin) than other classes of antibiotic. Some people may also find they are allergic to cefalexin, especially if they are sensitive to penicillin.


Your drug prescription is tailored for you. Do not alter dosage without checking with your doctor.

How taken/used Tablets, capsules, liquid.

Frequency and timing of doses 2–4 x daily.

Dosage range Adults 1–4g daily. Children Reduced dose according to age and weight.

Onset of effect Within 1 hour.

Duration of action 6–12 hours.

Diet advice None.

Storage Keep tablets and capsules in original container at room temperature; refrigerate liquid, but do not freeze, and keep for no longer than 10 days. Keep out of the reach of children and protect from light.

Missed dose Take as soon as you remember. If your next dose is due at this time, take both doses now.

Stopping the drug Take the full course. Even if you feel better, the original infection may still be present and may recur if treatment is stopped too soon.

Exceeding the dose An occasional unintentional extra dose is unlikely to be a cause for concern. But if you notice any unusual symptoms, or if a large overdose has been taken, notify your doctor.


Most people do not experience serious adverse effects while taking cefalexin. Diarrhoea is common but tends not to be severe. Nausea and vomiting are less common but are also usually not severe. Abdominal pain may also occur, and this should be reported to your doctor. The rarer adverse effects, such as rash, itching, swelling, and wheezing, are usually due to an allergic reaction and may necessitate stopping the drug. If you experience any of these effects, consult your doctor at once and stop taking the drug.


Probenecid This drug increases the level of cefalexin in the blood. The dosage of cefalexin may need to be adjusted accordingly.

Oral contraceptives Cefalexin may reduce the contraceptive effect of these drugs. Discuss with your doctor.


Be sure to tell your doctor if:

· You have a long-term kidney problem.

· You have had a previous allergic reaction to a penicillin or cephalosporin antibiotic.

· You have a history of blood disorders.

· You are taking other medicines.

Pregnancy No evidence of risk to the developing baby.

Breast-feeding The drug passes into the breast milk but at normal doses adverse effects on the baby are unlikely. Discuss with your doctor.

Infants and children Reduced dose necessary.

Over 60 Avoid. Increased risk of Clostridium difficile diarrhoea.

Driving and hazardous work No known problems.

Alcohol No known problems.


Cefalexin is usually given only for short courses of treatment.