Cephalexin: what it treats and how to use it

Cephalexin is a common antibiotic doctors prescribe for bacterial infections like skin infections, ear infections, throat infections, some lung infections and uncomplicated urinary tract infections. It’s in a group called cephalosporins and works by stopping bacteria from building cell walls.

How to take Cephalexin safely

Follow your prescriber's directions. Typical adult dosing is 250–500 mg every 6–12 hours. For tougher infections doctors may use up to 1–4 g per day, split through the day. For kids the usual range is 25–50 mg per kg per day divided every 6–12 hours. If you have kidney problems, your doctor will change the dose or the timing.

Take cephalexin with or without food. If it upsets your stomach, take it with a meal. Try to take doses evenly spaced to keep steady levels in your body. Don’t stop early even if you feel better—stopping can let the infection come back and breed resistant bacteria.

If you miss a dose, take it as soon as you remember unless it’s near the next dose; don’t double up to catch up.

Side effects, interactions, and warnings

Most people tolerate cephalexin well. Common side effects are diarrhea, nausea, stomach pain, and yeast infections. If you get severe diarrhea, bloody stools, or lots of belly pain, tell your doctor—this could be Clostridioides difficile, a serious reaction to many antibiotics.

If you’re allergic to penicillin or other cephalosporins, mention it. Some people who react to penicillin also react to cephalosporins, though many do not. A true allergic reaction includes hives, swelling of the face or throat, trouble breathing, or fainting—call emergency services if that happens.

Cephalexin can interact with other medicines. Probenecid raises cephalexin levels. If you take blood thinners like warfarin, your doctor will watch you closely because antibiotics can change INR. Always tell your provider about all prescription drugs, supplements, and herbal products you use.

Pregnancy and breastfeeding: Cephalexin is commonly used in pregnancy when needed, but check with your provider first. It passes into breast milk in small amounts; most babies tolerate it, but watch for diarrhea or rash.

Store the tablets at room temperature and keep liquid forms refrigerated if directed. Throw away any leftover medicine after the prescribed course—don’t keep it for later.

When to call the doctor: fever that gets worse, signs of allergic reaction, severe diarrhea, or no improvement after 48–72 hours for many infections. If an infection worsens quickly or you feel very unwell, seek care right away.

Using antibiotics responsibly helps them keep working. Take cephalexin exactly as prescribed, finish the course, and ask your doctor if you have questions about dosing, side effects, or interactions.