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

When you’re prescribed 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 keeps them from spreading. Unlike some stronger antibiotics, cephalexin is often one of the first choices for mild to moderate infections because it’s well-tolerated and widely available as a generic.

But cephalexin doesn’t work in a vacuum. It interacts with other common medications — especially antacids, over-the-counter products like Tums or Maalox that neutralize stomach acid. If you take an antacid within two hours of your cephalexin dose, your body might absorb up to 90% less of the antibiotic, making the treatment fail. That’s not a myth — it’s been shown in clinical studies. You also need to watch out for other antibiotics, like tetracycline or ciprofloxacin, which can compete for absorption or cause overlapping side effects. Mixing them without guidance can lead to unexpected problems.

People often assume all antibiotics are the same, but cephalexin has its own profile. It’s not great for deep tissue infections or resistant strains like MRSA. It’s also not the first pick for pneumonia or sinus infections anymore — those often need broader coverage. But for simple skin infections, bladder infections, or dental abscesses, it’s still a solid, affordable option. And because it’s taken multiple times a day, timing matters. Skipping doses or taking them too close together can lower your chances of clearing the infection.

Side effects are usually mild — upset stomach, diarrhea, or a bad taste in your mouth — but some people get allergic reactions, especially if they’re allergic to penicillin. It’s not a guarantee you’ll react, but it’s something your doctor should know before prescribing. And while cephalexin is safe for most adults, kids and seniors need careful dosing. Pregnant women can usually take it, but always check with your provider.

What you’ll find below is a collection of real, practical posts that dig into how cephalexin fits into the bigger picture of antibiotics, drug interactions, and infection treatment. You’ll see how it stacks up against other meds, why timing with antacids can make or break your treatment, and what to do if your infection doesn’t improve. These aren’t generic advice pieces — they’re based on actual clinical patterns and patient experiences. Whether you’re taking cephalexin now, were prescribed it in the past, or just want to understand why your doctor chose it over something else, this collection gives you the facts you need — no fluff, no hype, just what works.