When you take cefaclor, a second-generation cephalosporin antibiotic used to treat ear, lung, skin, and urinary tract infections. Also known as Cefaclor, it works well for many people—but not everyone reacts the same way. A cefaclor reaction can range from a mild rash to something life-threatening. If you’ve ever broken out in hives after taking it, or felt your throat close up, you’re not imagining it. These aren’t rare. Studies show up to 1 in 10 people report some kind of reaction, and about 1 in 100 of those could be serious.
Most reactions are mild: itching, nausea, diarrhea, or a red, blotchy skin rash. But here’s the thing—some people who think they’re just "sensitive" to antibiotics are actually having an allergic reaction, an immune system overresponse to the drug. This is different from side effects. Allergies can get worse with every dose. And if you’ve had a reaction to penicillin, your risk goes up. That’s because cephalosporins, a class of antibiotics that includes cefaclor, amoxicillin, and cefdinir. Also known as cephalosporin antibiotics, they share a similar chemical structure with penicillins. Cross-reactivity isn’t guaranteed, but it’s real enough that doctors won’t risk it.
Some people get delayed reactions—like a fever or swollen glands days after finishing the course. Others develop a condition called drug-induced lupus, where the body attacks its own tissues. These are rare, but they happen. If you’ve ever been told "it’s probably just a virus" after a cefaclor reaction, push back. Track your symptoms. Take a photo of any rash. Write down when you took the pill and when the reaction started. That info saves lives.
What’s not talked about enough is how often people stop antibiotics too soon because of fear. But stopping early can lead to worse infections. The key is knowing the difference between a nuisance side effect and a true emergency. If you’re wheezing, your tongue swells, or your blood pressure drops, call 911. If it’s just a rash and no breathing trouble, call your doctor. Don’t assume it’s harmless just because it’s "only" a rash.
Below, you’ll find real cases and expert insights on how cefaclor interacts with other drugs, how kids react differently, and what to do if you’ve had a reaction before. We’ve pulled together the most useful posts from people who’ve been there—so you don’t have to guess what’s normal and what’s dangerous.
Serum sickness-like reactions are delayed, non-allergic responses to antibiotics like cefaclor, often mistaken for true allergies. Learn the symptoms, how it's diagnosed, and why avoiding all penicillins is unnecessary.