Cephalexin: Uses, Side Effects, and What You Need to Know
When you have a bacterial infection—like a skin boil, a bad sinus infection, or a urinary tract infection—your doctor might reach for cephalexin, a first-generation cephalosporin antibiotic used to treat common bacterial infections. Also known as Keflex, it’s one of the most prescribed antibiotics in the U.S. because it works well, costs little, and is usually well tolerated. Unlike penicillin, it’s often safe for people with mild penicillin allergies, but that doesn’t mean it’s risk-free.
Cephalexin fights bacteria by breaking down their cell walls, which stops them from multiplying. It’s not a cure-all—it won’t touch viruses like the flu or colds. But for infections caused by staph, strep, or certain types of E. coli, it’s a go-to. You’ll typically take it two to four times a day for 7 to 14 days. Missing doses or stopping early can let the infection come back stronger, and it can even lead to antibiotic-resistant bugs. That’s why sticking to the full course matters more than you think.
Side effects are usually mild—upset stomach, diarrhea, or nausea—but some people get serious reactions. If you develop a rash, swelling, trouble breathing, or severe watery diarrhea, stop taking it and call your doctor right away. That could be a sign of an allergic reaction or a dangerous gut infection like C. diff. People with kidney problems may need a lower dose because cephalexin leaves the body through the kidneys. And if you’ve had a bad reaction to penicillin or another cephalosporin, talk to your doctor before starting this one—even if your allergy was years ago.
It’s not just about taking the pill. What you eat, what else you’re on, and even your age can change how cephalexin works. For example, antacids with magnesium or aluminum can make it less effective if taken at the same time. Alcohol doesn’t directly interact with it, but drinking while sick won’t help your body heal faster. Older adults might be more sensitive to side effects, and kids often get it in liquid form for ear infections or strep throat.
There are other antibiotics out there—amoxicillin, doxycycline, clindamycin—that might be better depending on your infection, allergies, or medical history. But cephalexin stays popular because it’s predictable. It doesn’t need special monitoring like some newer drugs. It’s been around since the 1960s, and doctors still trust it.
Below, you’ll find real-world guides on how cephalexin fits into broader antibiotic use—what to watch for, how it compares to other drugs, and what to do if something goes wrong. Whether you’re dealing with a skin infection, worried about side effects, or just trying to understand why your doctor chose this one, the posts here give you clear, no-fluff answers.
