Cephalexin (Keflex): What It Treats and How to Use It Safely

Cephalexin, commonly known by the brand name Keflex, is a widely used oral antibiotic for skin, ear, throat, and simple urinary tract infections. It’s been around for decades, but it still works well when chosen for the right bugs. If you’ve been prescribed cephalexin, here’s what you actually need to know—fast.

Cephalexin kills bacteria by disrupting their cell walls. That makes it good for common Gram-positive infections and some Gram-negative bugs. Doctors pick it for things like cellulitis, strep throat (if penicillin can’t be used), simple UTIs, and some dental infections. It’s not the right choice for complicated hospital infections or organisms known to be resistant.

Practical dosing and timing

Adults often take 250–500 mg every 6–12 hours depending on the infection. For many skin infections, 500 mg twice daily is common. Kids get weight-based doses—your prescriber will calculate mg per kg and split it across the day. Important: take doses evenly spaced to keep levels steady. If stomach upset hits, take it with food.

Kidney function matters. Cephalexin is cleared by the kidneys, so doctors lower the dose if you have reduced renal function. Don’t guess—ask your prescriber or pharmacist about adjustments if you have kidney disease.

Side effects, allergies, and safety tips

Most people tolerate cephalexin fine. The common side effects are mild: diarrhea, nausea, and occasional rash. If you get severe diarrhea, bloody stools, a high fever, or a fast-spreading rash, stop it and contact your clinician—those can be signs of a serious reaction or C. difficile infection.

If you’ve had a severe penicillin allergy (like anaphylaxis), mention it. Cross-reaction risk exists, so your doctor may choose a different class. Also tell your provider about other medications: probenecid can raise cephalexin levels, and certain health conditions may need dose changes.

Finish the full course unless told otherwise. Stopping early can let resistant bacteria survive and cause a comeback. If you miss a dose, take it as soon as you remember that day—don’t double up the next time.

Store cephalexin at room temperature, away from heat and moisture. For disposal, use a pharmacy take-back program or follow local guidelines—don’t toss large amounts in household trash or flush them.

Not working or allergic? Alternatives depend on the infection. For skin infections or respiratory bugs, clinicians may consider macrolides (like azithromycin) or doxycycline. For penicillin-allergic patients, the choice varies—talk to a prescriber to match the bug to the safest drug.

Buying antibiotics online? Use licensed pharmacies and check verification. If you’re unsure about a site or a dose, call a pharmacist or your clinic. Cephalexin is simple when used correctly—follow dosing, watch for problems, and ask questions if anything feels off.