How does this medication work? What will it do for me?

Ampicillin belongs to the group of medications called antibiotics, or more specifically penicillins. It is used alone or in combination with other antibiotics to treat and prevent infections (e.g., bladder infections, heart valve infections) caused by certain types of bacteria. This medication works by killing the bacteria or preventing their growth.

Under normal circumstances, your infection should begin to improve (reduced symptoms, temperature, etc.) within 24 to 48 hours. If you find this is not the case, contact your doctor.

Like other antibiotics, ampicillin is not effective against viruses such as those that cause the common cold.

Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. As well, some forms of this medication may not be used for all of the conditions discussed here. If you have not discussed this with your doctor or are not sure why you are using this medication, speak to your doctor. Do not stop using this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to use this medication if their doctor has not prescribed it.

What form(s) does this medication come in?

This medication is available as a 250 mg vial for injection.

How should I use this medication?

The dose and number of doses per day of ampicillin depend on the type of infection being treated or prevented. For most infections, the dose is usually given every 6 hours. To prevent heart valve infections, the usual adult dose is 2 grams as a single dose that is given 30 to 60 minutes before the procedure. For children and infants, the dose is usually based on body weight.

Many things can affect the dose of medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones listed here, do not change the way that you are using the medication without consulting your doctor.

Ampicillin capsules and liquid are best taken with a full glass (8 ounces) of water on an empty stomach (either 1 hour before or 2 hours after meals) unless otherwise directed by your doctor. Shake the liquid form of this medication well before each use and use an oral syringe to measure each dose of the liquid, as it gives a more accurate measurement than household teaspoons.

Ampicillin must be taken for the recommended duration of treatment, even if you are feeling better.

It is important to use this medication exactly as prescribed by your doctor. If you miss a dose, use it as soon as possible so that levels of the antibiotic will be kept as constant as possible in the blood and continue with your regular schedule. If it is almost time for your next dose, skip the missed dose and continue with your regular dosing schedule. Do not use a double dose to make up for a missed one.

Store the liquid form of ampicillin in the refrigerator, do not allow it to freeze and keep it out of the reach of children. Any portion of refrigerated medication that has not been consumed within 21 days should be discarded. Liquid ampicillin that has been left at room temperature is good for 7 days only.

Store the capsule form of the medication at room temperature away from heat and direct light and keep it out of the reach of children. Do not store ampicillin in the bathroom or near the kitchen sink, as moisture may cause the medication to break down.

Do not dispose of medications in wastewater (e.g. down the sink or in the toilet) or in household garbage. Ask your pharmacist how to dispose of medications that are no longer needed or have expired.

Who should NOT take this medication?

Do not use this medication if you:

  • are allergic to ampicillin, penicillin, or any ingredients of this medication
  • are allergic to other related medications (e.g., cephalexin, cloxacillin, cefaclor)

What side effects are possible with this medication?

Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

  • abdominal cramps
  • diarrhea
  • nausea
  • pain at the place of injection (injections form only)
  • skin rash
  • vaginal itching and discharge (yeast or fungal infection) - talk to your doctor or pharmacist about ways to reduce the likelihood of this side effect
  • vomiting

Although most of the side effects listed below don't happen very often, they could lead to serious problems if you do not seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

  • severe diarrhea
  • symptoms of low red blood cells (e.g., tiredness, shortness of breath, paleness)
  • symptoms of low white blood cells (e.g., fever, sore throat)
  • white patches in the mouth and/or tongue

Stop taking the medication and seek immediate medical attention if any of the following occur:

  • seizures (with high doses injected into a vein)
  • symptoms of a severe allergic reaction (e.g., hives; difficulty breathing; swelling of the face, mouth, tongue, or throat)

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Are there any other precautions or warnings for this medication?

Before you begin using a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use this medication.

Allergy: Allergic reactions to ampicillin are more common if you have a history of hay fever, hives, and other allergies. Reactions may include symptoms such as itching, hives, congestion, nausea, cramping, or diarrhea. Although much less common, more severe allergic reactions may include shortness of breath and swelling of the throat. If you experience these symptoms after taking this medication, stop taking the medication and get immediate medical attention.

If you have an allergy to this or related medications (e.g., penicillin, cephalexin), you should inform anyone involved with your medical care (e.g., doctor, pharmacist, nurse) and carry or wear easily accessible identification (such as a bracelet or necklace) alerting caregivers to the fact that your are allergic to penicillins.

Some people are "sensitive" (mild rash, upset stomach, etc.) to penicillins (e.g., amoxicillin, penicillin, ampicillin) while others are truly "allergic" (see symptoms above). As there may be times when it is most preferable to treat with penicillin (even if a person is "sensitive"), your doctor may test you to determine if you are truly allergic to this family of medications.

Blood cells: When ampicillin is taken for long periods of time, it can affect the amount of white blood cells, red blood cells, and platelets in the blood. If you are taking this medication for a long time, your doctor will monitor for this with blood tests.

Kidney function: If you have reduced kidney function, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Liver function: This medication may affect your liver function if you take it for long periods of time. Your doctor will monitor for this with blood tests if needed.

Severe diarrhea: As with other antibiotics, ampicillin may cause severe diarrhea that is associated with a bacteria called C. difficile or colitis (inflammation of the colon). If you develop severe diarrhea, especially if it contains blood or mucus, stop taking this medication and contact your doctor immediately.

Skin rash: People with infectious mononucleosis, acute lymphocytic leukemia (ALL), or cytomegalovirus (CMV) infection are more likely to experience a rash from ampicillin.

If you have any of these conditions, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Pregnancy: Ampicillin is safe to use during pregnancy.

Breast-feeding: This medication passes into breast milk. If you are a breast-feeding mother and are taking ampicillin, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children: When infants and children less than 16 years of age take this medication, their doctor may monitor their liver, kidneys, and blood cells periodically while they are taking this medication.

What other drugs could interact with this medication?

There may be an interaction between ampicillin and any of the following:

  • allopurinol
  • aminoglycosides (e.g., tobramycin, gentamicin)
  • atenolol
  • birth control pills containing estrogen
  • chloroquine
  • estrogens
  • fusidic acid
  • lanthanum
  • methotrexate
  • probenecid
  • tetracyclines (e.g., doxycycline, minocycline, tetracycline)
  • typhoid vaccine
  • warfarin

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

  • stop taking one of the medications,
  • change one of the medications to another,
  • change how you are taking one or both of the medications, or
  • leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications that you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.