How Cephalexin Works: Antibiotic Mechanism, Uses, and What You Need to Know

When you take cephalexin, a first-generation cephalosporin antibiotic used to treat bacterial infections. Also known as Keflex, it's one of the most prescribed antibiotics for skin, ear, and urinary tract infections. Unlike painkillers or anti-inflammatories, cephalexin doesn’t just calm symptoms—it kills the bacteria causing the problem. It does this by targeting the bacterial cell wall, a structure human cells don’t have. That’s why it’s effective without harming your body’s own cells.

beta-lactam antibiotics, a class of drugs that includes penicillins and cephalosporins like cephalexin work by blocking enzymes bacteria need to build strong cell walls. Without a solid wall, bacteria swell up and burst. This is called bactericidal action—meaning it kills bacteria, not just slows them down. That’s why doctors reach for cephalexin when they need fast, reliable results, especially for strep throat, cellulitis, or simple pneumonia.

It’s not magic, though. Cephalexin only works on certain types of bacteria, mostly gram-positive ones like Staphylococcus and Streptococcus. It won’t touch viruses, so it’s useless for colds or flu. And while it’s generally well-tolerated, some people get stomach upset or allergic reactions, especially if they’re allergic to penicillin. That’s why you never take leftover cephalexin for a new infection without checking with a doctor.

What makes cephalexin stand out isn’t that it’s the newest drug—it’s that it’s simple, cheap, and still works. Even with newer antibiotics like azithromycin or doxycycline, cephalexin remains a first-line choice in clinics worldwide. It’s in the WHO’s list of essential medicines for a reason. You’ll find it in use for kids with ear infections, diabetics with foot sores, and athletes with infected cuts.

It’s also not a drug you can skip doses on. Even if you feel better in two days, finishing the full course stops resistant strains from growing. That’s why it’s so important to take it exactly as prescribed. Skipping doses or stopping early doesn’t just hurt you—it makes antibiotics weaker for everyone.

Below, you’ll find real-world guides on how cephalexin compares to other antibiotics, what to watch for when using it, and how it fits into broader treatment plans for common infections. Whether you’re a patient, a caregiver, or just curious about how your medicine works, these posts give you the facts without the fluff.