Ampicillin: What it treats, how it works, and what to watch for

Ampicillin is a penicillin-type antibiotic you’ve likely heard of. Doctors use it to fight certain bacterial infections in the ear, throat, urinary tract, and gut. It kills bacteria by stopping them from building cell walls, which makes it useful for a range of common infections — but it won’t help viral illnesses like colds or the flu.

How people usually take ampicillin

Ampicillin comes as a pill, a chewable tablet, or an injection for hospitals. For oral forms, it’s often recommended on an empty stomach—about one hour before or two hours after a meal—to improve absorption. Typical adult oral doses are in the hundreds of milligrams several times a day; severe infections get higher IV doses in hospitals. Children’s doses are weight-based. Your prescriber will pick the exact dose and length of treatment based on the infection and your health.

Important: a prescription is required. Don’t use leftover pills or someone else’s prescription. Stopping early can let bacteria survive and become resistant.

Side effects, allergies, and safety tips

The most common side effects are mild stomach upset, diarrhea, and rash. If you get a red, itchy rash or hives, or you notice swelling of the face, lips, tongue, or trouble breathing, get emergency care — these can be signs of a serious allergic reaction to penicillin. Tell your doctor if you’ve ever had an allergic reaction to penicillin or cephalosporins.

Tell your provider about other medicines you take. Drugs such as probenecid, some blood thinners, or methotrexate can interact with antibiotics. If you have kidney problems, dosing may need adjustment. Pregnant or breastfeeding? Talk to your clinician — penicillins are commonly used in pregnancy but your doctor will confirm if ampicillin is right for you.

Antibiotic resistance is real. Many bacteria make enzymes called beta-lactamases that break down ampicillin. That’s why doctors may order a culture or choose a different antibiotic if resistance is likely. Never pressure a prescriber for antibiotics when they aren’t needed; misuse makes infections harder to treat later.

Storage is simple: keep pills in a cool, dry place and follow pharmacy instructions for liquid forms. Finish the full course exactly as prescribed. If you miss a dose, take it when you remember unless it’s almost time for the next dose — don’t double up.

If you’re wondering whether ampicillin is the right choice for your infection, ask for specifics: what bacteria are suspected, why this drug is chosen, expected side effects, and how long treatment should last. That short conversation helps you use antibiotics safely and get better faster.

Need more detailed answers about ampicillin or alternatives? Talk to your healthcare provider or pharmacist — they can match the facts to your situation and help you avoid risks.