Cefaclor Side Effects: What You Need to Know Before Taking It

When you’re prescribed Cefaclor, a second-generation cephalosporin antibiotic used to treat bacterial infections like ear infections, sinusitis, and urinary tract infections. Also known as a beta-lactam antibiotic, it works by stopping bacteria from building cell walls—effective, but not without risks. Many people take Cefaclor without issues, but side effects happen more often than you think. And not all of them are harmless.

The most common side effects? Upset stomach, diarrhea, nausea, and vomiting. These aren’t rare—they show up in about 1 in 10 people. But here’s what most guides don’t tell you: if your diarrhea turns watery, bloody, or lasts more than two days, it could be Clostridioides difficile, a dangerous gut infection triggered by antibiotics disrupting your natural bacteria. This isn’t just a tummy ache. It’s a medical red flag. Same goes for rashes or swelling. If your face, lips, or throat puff up after taking Cefaclor, stop immediately. That’s not an allergy you can tough out—it’s anaphylaxis waiting to happen. And yes, it’s happened before. Not to someone else. To real people. People who thought, "It’s just a pill. It’s fine."

Some side effects are sneaky. Like headaches, dizziness, or a metallic taste in your mouth. You might blame stress or coffee. But if you started Cefaclor a few days ago and suddenly can’t taste your food right, it could be the drug. Or maybe you’re feeling unusually tired, or your urine turns dark. That’s not normal. Your liver and kidneys are working overtime to process this antibiotic. If they’re struggling, your body will send signals. Listen.

And don’t assume you’re safe just because you’ve taken it before. Antibiotics can change how your body reacts over time. One dose might be fine. The next? Could trigger a delayed reaction—like a skin rash that shows up a week later. That’s not a coincidence. That’s your immune system reacting to the drug’s metabolites. And if you’ve ever had a reaction to penicillin? You’re at higher risk. Cefaclor and penicillin share similar structures. Cross-reactivity isn’t just a theory—it’s documented in clinical studies.

What about kids? Cefaclor is often given to children for ear infections. Parents need to watch for fussiness, loss of appetite, or unusual sleepiness. These aren’t just "being a kid" signs. They could be early signs of something deeper. And if your child develops a fever after starting Cefaclor? That’s not the infection coming back. It could be a drug reaction.

There’s also the long-term question. Antibiotics like Cefaclor don’t just kill bad bacteria—they wipe out the good ones. That’s why probiotics are often recommended. But even then, your gut microbiome might not bounce back fully. Studies show changes can last months. And that affects everything—from digestion to mood to immunity.

So what do you do? Don’t skip your dose if you’re feeling okay. But if you notice anything new—especially if it’s persistent or worsening—don’t ignore it. Call your doctor. Take a photo of a rash. Write down when the diarrhea started. Track your energy. These details matter. They help your doctor decide: is this a side effect, or something worse?

Below, you’ll find real cases and practical advice from people who’ve been there. No fluff. No marketing. Just what works, what doesn’t, and what you need to watch for when you’re on Cefaclor.