Cephalexin (Keflex) — What You Need to Know

Cephalexin is a common oral antibiotic used for many simple infections: skin infections, ear infections, throat infections and some urinary tract infections. You’ll often see it under the brand name Keflex. It’s a first-generation cephalosporin — works by stopping bacteria from building strong cell walls so they die off. Doctors prescribe it a lot because it’s usually effective and well tolerated.

Quick facts and common uses

Typical adult dosing is 250–500 mg every 6–12 hours depending on the infection. For example, mild skin or throat infections often use 250–500 mg every 6–8 hours; some urinary infections can be treated with 500 mg twice daily. For children, the usual range is about 25–50 mg per kg of body weight per day, split into doses. Your prescriber will pick the exact dose and how long you need it.

If you have kidney problems, doses often need to be lowered or given less often. Tell your doctor about any kidney disease so they can adjust the plan. Don’t try to guess doses — ask your healthcare provider or pharmacist.

How to take it, side effects, allergies, and buying tips

Take cephalexin with or without food. If it gives you an upset stomach, try taking it with food or milk. Finish the entire course even if you feel better, unless your doctor tells you to stop. Stopping early can let bacteria come back stronger.

Common side effects include nausea, stomach pain, and diarrhea. You may also get yeast infections or mild rashes. Rare but serious reactions include severe allergic responses (hives, swelling, trouble breathing) or severe diarrhea caused by C. difficile. If you get high fever, bloody diarrhea, or breathing problems, get medical help right away.

Allergy note: if you’re allergic to penicillin, tell your doctor. Most people with penicillin allergy can still take cephalexin, but cross-reaction is possible. Your provider will assess your allergy history before prescribing.

Drug interactions: probenecid can raise cephalexin levels. Some antacids or iron supplements may reduce absorption of some antibiotics — give a 2-hour gap if you take antacids or iron, or check with your pharmacist for specifics.

Buying tips: only use a licensed pharmacy and always have a valid prescription. Avoid sites that sell without prescriptions or offer suspiciously low prices. Look for clear contact details, pharmacy license info, and real customer reviews. If ordering from another country, check your local import rules and allow extra time for delivery. When in doubt, call a pharmacist to confirm you’re getting the right strength and instructions.

Practical tip: keep a photo or printed copy of your prescription and the dosing instructions. If your symptoms don’t improve within 48–72 hours or they get worse, contact your doctor — you may need a different antibiotic or further tests.