Ampicillin: Uses, Side Effects, and How It Compares to Other Antibiotics

When you’re dealing with a bacterial infection, your doctor might reach for ampicillin, a broad-spectrum antibiotic in the penicillin family used to treat infections like urinary tract infections, ear infections, and certain types of pneumonia. Also known as a semi-synthetic penicillin, it works by stopping bacteria from building cell walls, which kills them or stops them from multiplying. It’s not new, but it’s still widely used because it’s effective, affordable, and works against a decent range of common bugs.

Ampicillin is closely related to amoxicillin, a more modern cousin that’s better absorbed by the gut and often preferred for oral use. Both are penicillins, but amoxicillin tends to be the go-to for kids and outpatients because it’s easier to take and causes fewer stomach issues. penicillin, the original antibiotic from the 1940s, is narrower in scope—ampicillin covers more types of bacteria, including some that penicillin can’t touch. That’s why doctors choose ampicillin when they need broader coverage, like in suspected mixed infections.

It’s not a magic bullet. Ampicillin won’t work on viruses, and it’s useless against drug-resistant strains like MRSA. Some people have allergic reactions—rash, itching, or worse—especially if they’ve had issues with penicillin before. Common side effects include diarrhea, nausea, and yeast infections, which happen because it wipes out good bacteria along with the bad. That’s why it’s important not to take it unless you really need it, and never to save leftover pills for later.

You’ll find ampicillin used in real-world cases like uncomplicated bladder infections, sinus infections, and even some types of meningitis in newborns. It’s often given as a shot in hospitals, but pills are common for milder cases. It’s also sometimes paired with other drugs, like sulbactam, to fight tougher bacteria that produce enzymes to break down penicillins.

Below, you’ll find detailed comparisons and real patient-focused guides on how ampicillin stacks up against other antibiotics like Bactrim, cefprozil, and cefadroxil. You’ll see when it’s the best choice, when it’s not, and what to watch out for—no fluff, just clear, practical info to help you understand your treatment.