Cefalexin is a cephalosporin, a close relative of penicillin. It is commonly used for urinary, skin and respiratory infections, including in pregnancy, and is sometimes an option for people with a mild penicillin allergy.
Urinary tract infections including in pregnancy, skin and soft tissue infections, chest infections, and some ear and bone infections. It is also used at low dose to prevent recurrent UTIs.
Usually two to four times daily, with or without food — though food reduces stomach upset. Space doses evenly and finish the course.
Suspension should be shaken well, measured with the syringe or spoon provided, and usually kept in the fridge — check the label.
Cephalosporins are structurally related to penicillins, so there is a small chance of cross-reactivity. In practice, most people with a penicillin allergy label can take cefalexin safely, but anyone who has had a severe reaction — anaphylaxis, swelling of the throat, or a severe blistering rash — to a penicillin should avoid cephalosporins unless a specialist advises otherwise.
Tell your prescriber exactly what happened when you reacted; the detail changes the decision.
Common side effects: nausea, diarrhoea, stomach ache and thrush. Get urgent help for swelling of the face or throat, difficulty breathing, or a widespread blistering rash. Report severe or bloody diarrhoea during or after the course.
It can be used in pregnancy and breastfeeding where indicated.
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