Cefaclor vs Amoxicillin: Key Differences and When to Choose Each

When you’re prescribed an antibiotic, it’s easy to assume all are the same. But cefaclor, a second-generation cephalosporin antibiotic used to treat respiratory, ear, and skin infections works differently from amoxicillin, a penicillin-class antibiotic commonly used for sinus, throat, and urinary tract infections. They’re both broad-spectrum, but that’s where the similarity ends. One might clear up your ear infection faster; the other could be safer if you’ve had reactions to penicillin before. Choosing between them isn’t about which is "stronger"—it’s about matching the bug, your history, and your body’s response.

Many people think if amoxicillin didn’t work, cefaclor is the next step. But that’s not always true. Cefaclor is more resistant to certain bacterial enzymes that break down penicillin-based drugs like amoxicillin. That means if your infection is caused by a strain that’s learned to fight off amoxicillin, cefaclor might still work. On the flip side, if you’re allergic to penicillin, cefaclor could still cause a reaction—about 10% of people with penicillin allergies also react to cephalosporins like cefaclor. So, your doctor doesn’t just pick one over the other randomly. They look at your past reactions, the type of infection, and even local resistance patterns. For example, amoxicillin is still first-line for strep throat because it’s cheap, effective, and has decades of proven results. Cefaclor? It’s often used when that doesn’t cut it, or when you need something that lasts longer in your system.

Side effects matter too. Amoxicillin can cause diarrhea or yeast infections more often, while cefaclor is more likely to trigger nausea or a rash. Neither is "better"—just different. If you’ve had stomach issues with one, switching to the other might help. But don’t guess. The antibiotic side effects, ranging from mild GI upset to serious allergic reactions can vary by person, and mixing them up can lead to resistance or worse. That’s why your doctor checks your history, not just the symptoms.

These aren’t just random pills. They’re tools shaped by decades of research, bacterial evolution, and real-world use. The posts below dig into how these two antibiotics compare in actual cases—when one wins, when they’re equally matched, and what to do if things go sideways. You’ll find real stories, side-by-side breakdowns of effectiveness, and what to watch for after you start taking them. No fluff. Just what you need to understand why your doctor picked one over the other—and what to ask next time.