Ampicillin: What It Does and How to Use It Safely

Ampicillin is a common antibiotic used to treat bacterial infections. It kills bacteria by stopping their cell wall from forming. Doctors prescribe it for ear infections, urinary tract infections, bronchitis, and some more serious infections when the bacteria are sensitive to it. You can get it as pills, a liquid, or an injection.

How ampicillin works and when it’s used

Ampicillin belongs to the penicillin family. It works by blocking a key step bacteria need to build a protective wall. That makes bacteria burst and die. Doctors choose ampicillin when tests show the germ responds to it, or when a patient needs broad coverage for common bacteria. It is often used for ear and throat infections, mild pneumonia, urinary infections, and some gastrointestinal infections. In hospitals it may be given by injection for more severe cases. Dosage depends on age, weight, and infection type. Adults often take 250–500 mg every 6 hours by mouth. Children get weight-based doses. Always follow the exact dose your clinician gives you.

Side effects, interactions, and practical tips

Most people tolerate ampicillin well. Common side effects include diarrhea, nausea, and skin rash. If you get a severe allergic reaction such as hives, swelling, trouble breathing, or a high fever with a rash, stop the drug and seek emergency care. Ampicillin can cause a characteristic rash in people with mononucleosis. Tell your doctor about all medicines you take. Some drugs and conditions raise the risk of bad reactions. Probiotics or yogurt can help prevent antibiotic diarrhea. Finish the full course even if you feel better; stopping early can let bacteria return and become resistant. If vomiting prevents you from keeping pills down, contact your provider; they may switch the route to injection.

Store tablets in a cool dry place and keep liquid forms refrigerated if the label says so. Do not share antibiotics or use leftover pills for a new illness. Pregnant or breastfeeding people should discuss risks and benefits with their clinician before starting ampicillin. For kids, dosing is precise, so use a proper measuring device for liquid medicine.

If you miss a dose, take it as soon as you remember unless it is almost time for the next dose. Do not double up. Seek care if symptoms worsen, if you have high fever, severe diarrhea, blood in stool, or signs of an allergic reaction. Your clinician can advise on tests to confirm the infection and whether ampicillin remains the right choice.

Antibiotic resistance is a real concern. If symptoms do not improve after 48–72 hours, contact your provider; they may order a culture or switch antibiotics. Never pressure a doctor for antibiotics for viral infections like colds. If you've had liver or kidney disease, doses may need adjusting. Keep a list of past drug allergies and past antibiotic reactions. When disposing, mix leftover pills with coffee grounds and throw in the trash or use a take-back program. Pharmacy take-back is safest. Stay informed always.