Cephalexin: What It Is, How It Works, and What You Need to Know

When your doctor prescribes cephalexin, a first-generation cephalosporin antibiotic used to treat bacterial infections like skin boils, strep throat, and urinary tract infections. Also known as Keflex, it works by stopping bacteria from building cell walls, which kills them or stops them from spreading. Unlike some broad-spectrum antibiotics, cephalexin targets specific types of bacteria—mostly Gram-positive ones—making it a go-to for common infections without overloading your system.

Many people compare cephalexin to amoxicillin, a penicillin-class antibiotic often used for ear infections, sinusitis, and pneumonia. Both are oral, affordable, and effective, but cephalexin is often chosen when someone has a mild penicillin allergy or when the infection doesn’t respond to amoxicillin. It’s also one of the few antibiotics that stays stable in the body long enough to be taken just twice a day, which helps with sticking to the schedule. But here’s the catch: it doesn’t work on viruses. Taking it for a cold or flu won’t help—and might make future infections harder to treat.

Side effects are usually mild—stomach upset, diarrhea, or nausea—but if you develop severe diarrhea with blood or mucus, stop taking it and call your doctor. That could be a sign of C. diff, a dangerous gut infection linked to antibiotic use. People with kidney problems need lower doses because cephalexin clears through the kidneys. And if you’ve had an allergic reaction to penicillin or another cephalosporin, talk to your doctor before starting. Cross-reactivity isn’t guaranteed, but it’s not rare either.

Generic versions of cephalexin are widely available and just as effective as the brand name. That’s why it’s one of the most prescribed antibiotics in Canada—cheap, reliable, and easy to find. But like all antibiotics, its power depends on using it right. Finish the full course, even if you feel better. Skip doses, and you risk leaving behind the toughest bacteria to multiply and spread.

What you’ll find in the posts below isn’t just more about cephalexin. You’ll see how it fits into the bigger picture of antibiotics—how it compares to others, how diet affects its absorption, what happens when you switch from brand to generic, and how some people end up with unexpected side effects like sweating or yeast infections. These aren’t random stories. They’re real experiences from people who’ve used cephalexin, or similar drugs, and lived to tell the tale. Whether you’re starting it now or just wondering why your doctor picked it over something else, this collection gives you the straight facts—not the hype.