Keflex: What It Is, How It Works, and What You Need to Know About Antibiotics

When you hear Keflex, a first-generation cephalosporin antibiotic used to treat bacterial infections like skin boils, urinary tract infections, and respiratory bugs. Also known as cephalexin, it’s one of the most prescribed antibiotics in outpatient settings—especially when penicillin isn’t an option. It doesn’t work on viruses, but for many common bacterial problems, it’s fast, affordable, and effective.

Keflex belongs to the cephalosporin class of antibiotics, which are cousins to penicillin. That means if you’re allergic to penicillin, you might still react to Keflex—about 10% of people do. It kills bacteria by breaking down their cell walls, which is why it works well on skin infections, ear infections, and some types of pneumonia. But it’s not a magic bullet. Many strains of bacteria have grown resistant to it, especially in hospitals or after repeated use.

You’ll often see Keflex paired with other treatments. For example, if you’re treating a sinus infection, your doctor might check if you’ve taken antibiotics recently—because if you have, Keflex might not work anymore. It’s also commonly used after dental work to prevent infection, or for cellulitis that won’t clear with over-the-counter care. But it’s not always the first choice anymore. Newer antibiotics like amoxicillin-clavulanate or doxycycline often get picked first, depending on the infection type and local resistance patterns.

Side effects are usually mild—upset stomach, diarrhea, or a rash—but serious reactions like severe allergic responses or C. diff colitis can happen. If you’ve ever had diarrhea that lasted more than a few days after finishing Keflex, that’s not normal. It could be a sign of antibiotic disruption in your gut, and you should get it checked. Also, don’t skip doses or stop early just because you feel better. That’s how resistant bacteria start.

What’s interesting is how Keflex fits into the bigger picture of antibiotic use. Many people don’t realize that antibiotic resistance isn’t just a hospital problem—it’s driven by everyday choices. Taking antibiotics for a cold, saving leftover pills for next time, or not finishing the full course all contribute. And Keflex is no exception. In fact, it’s one of the top antibiotics found in water systems because it’s so widely used and not fully filtered out.

There’s also a cost angle. Keflex is usually cheap—often under $10 for a full course at most pharmacies. But generic versions vary in quality depending on where they’re made. Some patients report different side effects between brands, even if they’re both labeled as cephalexin. That’s because inactive ingredients can differ, and your body might react to those.

What you’ll find in the posts below isn’t just a list of articles about Keflex. It’s a collection of real, practical insights from people who’ve used antibiotics like this—and seen the consequences. You’ll read about how antibiotics interact with other meds, how liver health affects how your body handles them, why some people get rashes while others don’t, and how to spot when an antibiotic isn’t working. There are also guides on how to avoid common mistakes, what to ask your pharmacist, and how to tell if you’re dealing with an infection that actually needs antibiotics—or something else entirely.

Whether you’re taking Keflex now, were prescribed it in the past, or just want to understand how antibiotics really work in everyday life—this collection gives you the facts without the hype. No fluff. No marketing. Just what you need to know to use antibiotics safely and wisely.