Cephalexin: What It Is, How It Works, and What Alternatives You Should Know

When you’re dealing with a stubborn skin infection, a bad sinus cold, or a urinary tract issue, your doctor might reach for cephalexin, a first-generation cephalosporin antibiotic used to treat bacterial infections like cellulitis, strep throat, and bladder infections. Also known as Keflex, it’s one of the most prescribed antibiotics in the U.S. because it’s effective, affordable, and generally well-tolerated. Unlike some stronger antibiotics that hit everything in sight, cephalexin targets specific bacteria — mostly gram-positive ones like staph and strep — which means it’s less likely to wreck your gut flora if used properly.

But cephalexin isn’t the only option. If you’ve had an allergic reaction to penicillin, your doctor might still prescribe it — cross-reactivity is rare, but not impossible. If it doesn’t work, or if your infection is caused by something tougher like MRSA or certain gram-negative bugs, alternatives like amoxicillin, a penicillin-class antibiotic often used for ear infections and pneumonia, or doxycycline, a tetracycline antibiotic effective against acne, Lyme disease, and some respiratory infections might be better choices. You’ll also see clindamycin, an antibiotic used when patients can’t take penicillin or cephalosporins, especially for skin and soft tissue infections in the mix. These aren’t just random swaps — each has a different strength, dosing schedule, and side effect profile.

What you won’t find in most patient brochures is how often people stop taking cephalexin too early because they feel better. That’s how resistant bacteria start. Or how it can cause diarrhea, rashes, or, rarely, serious gut infections like C. diff. You also won’t hear how much cheaper generic cephalexin is compared to brand-name Keflex — and how insurance sometimes blocks it unless you prove you’ve tried something else first. The posts below dig into all of that: how to spot when cephalexin is the right call, when it’s not, what to do if it doesn’t work, and how to handle side effects without panicking. You’ll also see how it stacks up against other antibiotics in real-world use — not just in textbooks, but in clinics, pharmacies, and homes where people are actually trying to get better.