Cephalexin

Infections

Also known as Keflex

Cephalexin is a cephalosporin antibiotic often used for skin infections, urinary tract infections, strep throat, and bone infections. It's a close cousin of penicillin, so if you've ever reacted to penicillin, your doctor needs to know — a small number of people react to both. It only kills bacteria, so it won't help with viruses.

How to take it

When

Space doses evenly through the day, exactly as prescribed.

Food

Works with or without food. A meal can settle your stomach if it bothers you.

Avoid

Tell your doctor about any penicillin allergy before starting — some people react to both.

Finish it

Take the full course, even when you feel better. Stopping early can bring the infection back.

Missed a dose?

Take it as soon as you remember. If your next dose is coming up soon, skip the missed one and stay on schedule. Never double up.

Common side effects

Diarrhea
Nausea or upset stomach
Headache
Yeast infections

Call a doctor if

Trouble breathing, swelling of the face or throat, or hives — this can be a serious allergic reaction. Get emergency help now.
Severe watery or bloody diarrhea, during treatment or even weeks after — this can be a serious gut infection (C. diff). Call your doctor; don't just take anti-diarrhea medicine.
A widespread rash, blistering, or peeling skin — stop and call your doctor right away.
Very dark urine or much less urine than usual.

Educational only. This summary is drawn from public FDA labeling and MedlinePlus and simplified for readability. Your prescription label and your pharmacist always come first — doses and instructions vary from person to person.