Cephalexin (Keflex): Uses, Side Effects, and Warnings

ImportantThis page is general information, not a prescription. Don't start, stop, or change a medicine without talking to your provider or pharmacist.

Overview

It kills bacteria. It doesn't work on viruses.

What it's used for

Skin infections, such as cellulitis
Strep throat
Urinary tract infections
Ear infections
Bone infections

How to take it

Take it with or without food, spaced evenly through the day.
Finish the full course even if you feel better.
Shake the liquid and keep it in the fridge.

Your dose depends on your health and other medicines. Always follow your prescription label, and ask your pharmacist if anything is unclear.

Side effects

Common side effects

Diarrhea
Nausea
Stomach upset

Call 911Swelling of the face, lips, or throat, hives, or trouble breathing

Call 911A blistering, peeling, or widespread red rash, especially with fever

Call your provider todaySevere watery or bloody diarrhea, even weeks after finishing (possible C. diff infection)

Warnings

Tell your provider about any penicillin or cephalosporin allergy.

Other medicines, foods, and alcohol

Metformin levels may rise.
Probenecid raises cephalexin levels.

Tell your provider and pharmacist about every medicine, vitamin, and supplement you take.

Pregnancy and breastfeeding

Commonly used in pregnancy and breastfeeding when needed.

Missed doses, overdose, and storage

If you miss a dose

Take it as soon as you remember. If it's almost time for the next dose, skip the missed one. Don't double up, and still finish the full course.

If someone takes too much

Call Poison Control at 1-800-222-1222 or get help online at poison.org. Call 911 if the person collapses, has a seizure, has trouble breathing, or can't be woken.

Storing it

Store at room temperature, away from heat and moisture (not in the bathroom), and out of reach of children and pets.

Conditions it's used for

Sources

Last updated 2026-11-13.

Cephalexin