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

When you’re prescribed Keflex, a first-generation cephalosporin antibiotic used to treat bacterial infections like skin boils, urinary tract infections, and respiratory tract infections. Also known as cephalexin, it works by stopping bacteria from building cell walls, which kills them or stops them from multiplying. It’s one of the most commonly prescribed antibiotics in the U.S.—cheap, effective, and usually well-tolerated. But it’s not right for every infection, and knowing when it’s the best choice matters.

People often confuse Keflex with other antibiotics like amoxicillin, a penicillin-type drug used for ear infections, sinusitis, and strep throat, or doxycycline, a tetracycline antibiotic effective against acne, Lyme disease, and some respiratory bugs. Keflex is narrower in scope than amoxicillin—it doesn’t cover some of the same bacteria, especially those causing sinus or ear infections in kids. But it’s often preferred if you’re allergic to penicillin. Unlike doxycycline, it doesn’t make your skin sun-sensitive or cause stomach upset as often. Still, it can cause diarrhea, nausea, or yeast infections, and overuse leads to resistance.

What’s missing from most doctor’s office conversations is how often Keflex is prescribed when it’s not needed. Many upper respiratory infections are viral, and antibiotics like Keflex won’t help. Yet it’s still handed out because patients expect something, or doctors want to avoid follow-up visits. The real value comes when you know what Keflex can and can’t do. If you’ve had a skin infection that didn’t respond, you might need a different class of antibiotic. If you’re on Keflex and your symptoms get worse after a few days, that’s a red flag—not a sign you need more, but that you might need something else.

You’ll find posts here that compare Keflex to other antibiotics like amoxicillin, explain why some people get diarrhea after taking it, and show how to tell if your infection is bacterial or viral. There are also guides on what to do if you’re allergic to penicillin and need a safe alternative, and how to avoid the trap of using antibiotics when they won’t help. These aren’t just drug lists—they’re real-world tools for understanding when Keflex makes sense, when it doesn’t, and what to ask your doctor next time you’re handed a prescription.