Ampicillin – an antibiotic in the penicillin group of drugs

Ampicillin is an antibiotic in the penicillin group of drugs that fights bacteria in your body.

Drug Uses

Ampicillin is an antibiotic in the penicillin group of drugs. It fights bacteria in your body. Ampicillin 250mg is used to treat many different types of infections caused by bacteria, such as ear infections, bladder infections, pneumonia, gonorrhea, and E. coli or salmonella infections.

How to use

Use Ampicillin as directed by your doctor.

Take Ampicillin by mouth at least one-half hour before or two hours after eating.

Take Ampicillin with a full glass of water (8 oz/240 mL).

Take Ampicillin on a regular schedule to get the most benefit from it. Taking Ampicillin at the same time each day will help you remember to take it.

To clear up your infection completely, use Ampicillin for the full course of treatment. Keep using it even if you feel better in a few days.

Ask your health care provider any questions you may have about how to use Ampicillin.

Drug Class and Mechanism

Ampicillin is a penicillin antibiotic. It works by killing sensitive bacteria by interfering with the formation of the bacteria’s cell wall while it is growing. This weakens the cell wall and it ruptures, resulting in the death of the bacteria.

Missed Dose

If you miss a dose of Ampicillin and are taking it regularly, take it as soon as possible. If it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not take 2 doses at once.


Store Ampicillin at room temperature, between 68 and 77 degrees F (20 and 25 degrees C). Store it away from heat, moisture, and light. Do not store it in the bathroom. Keep it in a tight, light-resistant container. Keep Ampicillin out of the reach of children and away from pets.


Do not use Ampicillin if:

  • you are allergic to any ingredient in Ampicillin or any other penicillin antibiotic (e.g., amoxicillin).

Contact your doctor or health care provider right away if any of these apply to you.

Some medical conditions may interact with ampicillin. Tell your doctor or pharmacist if you have any medical conditions, especially if any of the following apply to you:

  • If you are pregnant, planning to become pregnant, or are breast-feeding,
  • If you are taking any prescription or non-prescription medicine, herbal preparation, or dietary supplement,
  • If you have allergies to medicines, foods, or other substances,
  • If you have a stomach infection, diarrhea, or mononucleosis (“mono”),
  • If you have had a severe allergic reaction (e.g., a severe rash, hives, breathing difficulties, dizziness) to a cephalosporin antibiotic (e.g., cephalexin) or other beta-lactam antibiotic (e.g., imipenem), do not use this medication.

Some MEDICINES MAY INTERACT with Ampicillin . Tell your health care provider if you are taking any other medicines, especially any of the following:

  • tetracyclines (e.g., doxycycline) because they may decrease ampicillin’s effectiveness.
  • Provigil (Modafinil) because it causes narcolepsy.
  • Allopurinol because the risk of skin rash may be increased.
  • anticoagulants (heparin, warfarin) or methotrexate because the risk of their side effects may be increased by ampicillin.
  • birth control pills because their effectiveness may be decreased by ampicillin.