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

When you’re prescribed cephalexin, a first-generation cephalosporin antibiotic used to treat common bacterial infections like skin boils, strep throat, and urinary tract infections. Also known as Keflex, it’s one of the most widely prescribed antibiotics in the U.S. because it’s affordable, effective, and well-tolerated by most people. But it’s not the only option—and knowing how it stacks up against others can help you avoid side effects or resistance down the line.

Cephalexin works by breaking down the cell walls of bacteria, which stops them from multiplying. It’s most effective against Gram-positive bugs like Staphylococcus and Streptococcus, which is why doctors reach for it for skin infections or ear infections. But it doesn’t touch all bacteria. For example, if you have a sinus infection caused by resistant strains or a urinary tract infection from E. coli that’s become immune, cephalexin might not cut it. That’s where alternatives like amoxicillin, a penicillin-class antibiotic often used for similar infections but with broader coverage or doxycycline, a tetracycline that works well for acne, Lyme disease, and some respiratory infections come in. These aren’t just random substitutes—they’re chosen based on the type of infection, your allergies, and even your past reactions to antibiotics.

Side effects are usually mild—stomach upset, diarrhea, or nausea—but some people develop serious allergic reactions, especially if they’re allergic to penicillin. That’s why it’s important to know your history. And if you’ve taken cephalexin before and it didn’t work, or if you got a rash or yeast infection after finishing the course, you’re not alone. Many patients end up switching to other antibiotics like clindamycin, often used when someone can’t take cephalosporins or penicillins or trimethoprim-sulfamethoxazole, a combo drug effective for stubborn UTIs and some skin infections. The key isn’t just finding the strongest drug—it’s finding the right one for your body and your infection.

You’ll also find that cost and availability vary. Cephalexin is cheap because it’s been around for decades and generics are everywhere. But that doesn’t mean it’s always the best choice. Some infections respond better to newer antibiotics with fewer side effects, even if they cost more. And if you’ve ever wondered why your doctor switched you from cephalexin to something else after a few days, it’s often because they saw how your body reacted—or didn’t react.

Below, you’ll find real comparisons between cephalexin and other antibiotics, breakdowns of side effects you might not know about, and what to do if your infection doesn’t improve. Whether you’re taking it now, had a bad experience before, or just want to understand why your doctor picked it, this collection gives you the facts without the fluff.