Keflex (cephalexin): quick, practical facts

Keflex is the brand name for cephalexin, an oral cephalosporin antibiotic doctors use for common bacterial infections — think skin infections, strep throat, ear infections, and simple urinary tract infections. It works by damaging the bacteria’s cell wall so the bug can’t survive. Doctors pick Keflex when lab tests or symptoms suggest the infection will respond to a cephalosporin.

Typical adult doses are 250–500 mg every 6–12 hours depending on how serious the infection is. For tougher cases a prescriber might use 1 g every 12 hours. Children get weight-based doses (usually 25–50 mg/kg/day divided). If you have kidney problems your provider will lower the dose or space it out more — don’t adjust on your own.

Side effects and red flags

Common side effects are stomach upset, diarrhea, and a mild rash. Serious problems are less common but worth watching for: severe watery or bloody diarrhea, high fever, a spreading rash with blisters, trouble breathing, or swelling of face and throat. Those could mean C. difficile infection or an allergic reaction — get urgent care if they happen.

If you say you’re allergic to penicillin, mention it before taking Keflex. Many people with penicillin allergy can still take cephalosporins, but cross-reaction is possible. Your clinician may ask questions or recommend testing if needed.

How to use Keflex well

Take Keflex exactly as prescribed, with or without food. Finish the full course even if you feel better after a day or two — stopping early risks relapse and resistance. If you miss a dose, take it when you remember unless it’s almost time for the next dose; don’t double up.

Avoid using antibiotics for viral illnesses like colds or the flu. Antibiotics only help bacterial infections and overuse makes future infections harder to treat. If symptoms don’t improve in 48–72 hours, call your provider — they may need to check the diagnosis or switch medicines based on tests.

Keflex has few major drug interactions, but tell your clinician about blood thinners and other prescription meds. Store tablets at room temperature away from moisture. Dispose of leftovers safely — don’t keep old antibiotics “just in case.”

Thinking of buying Keflex online? Use pharmacies that require a valid prescription, show a physical address, and list a licensed pharmacist contact. Avoid sites selling antibiotics without prescriptions or offering suspiciously low prices. Read our guides on safe online pharmacies and antibiotic alternatives if you want more help choosing a trusted source.

Questions about whether Keflex is right for your infection, dosing during pregnancy or breastfeeding, or allergy concerns? Talk to your clinician — the right antibiotic matters for both safety and cure.