Ampicillin | Side Effects, Dosage, Uses & More
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Generic Name:

ampicillin, Oral capsule

All Brands

  • Principen (Discontinued)
A discontinued drug is a drug that has been taken off the market due to safety issues, shortage of raw materials, or low market demand.
SECTION 1 of 5

Highlights for ampicillin

Oral capsule
1

Ampicillin is used to treat infections that are caused by a certain type of bacteria.

2

Ampicillin is available as capsule and suspension you take by mouth. It’s also available in an intravenous form, which is only given by a healthcare provider.

3

Ampicillin is only available as a generic drug.

IMPORTANT INFORMATION

Finish your full course of treatment

Finish all of your medication as prescribed by your doctor. Don’t stop taking your drug or skip doses if you start to feel better. Doing so could make your infection last longer. You could also become resistant to the drug. That means if you get another bacterial infection, ampicillin may not work to treat it.

Diarrhea

This drug may cause diarrhea. Call your doctor if you have bloody or watery diarrhea with or without stomach cramps and fever after you stop taking this drug.

What is ampicillin?

Ampicillin is a prescription drug. It comes as an oral capsule and oral suspension. It’s also available in an intravenous (IV) form, which is only given by a healthcare provider.

Ampicillin is only available as a generic drug.

This drug may be used as part of a combination therapy. This means you may need to take it with other medications.

Why it's used

Ampicillin is used to treat infections that are caused by a certain type of bacteria.

How it works

Ampicillin belongs to the drug class penicillin

See Details

How it works

Ampicillin belongs to the drug class penicillin. A class of drugs is a group of medications that work in a similar way. These drugs are often used to treat similar conditions.

This drug works by killing bacteria to stop the infection from growing in your body.

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SECTION 2 of 5

ampicillin Side Effects

Oral capsule

More common side effects

Ampicillin doesn’t cause drowsiness. The more common side effects of ampicillin can include:

  • nausea

  • vomiting

  • diarrhea

  • rash

If these effects are mild, they may go away within a few days or a couple of weeks. If they’re more severe or don’t go away, talk to your doctor or pharmacist.

Serious side effects

Call your doctor right away if you have serious side effects. Call 911 if your symptoms feel life-threatening or if you think you’re having a medical emergency. Serious side effects and their symptoms can include the following:

  • Allergic reactions. Symptoms can include:

    • flu-like symptoms, such as fever and body aches
    • painful red or purple rash that spreads
    • blisters that could lead to skin breakdown
  • Diarrhea that lasts after you stop taking the drug. Symptoms can include:

    • diarrhea with or without stomach cramps
    • diarrhea with a fever
Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs affect each person differently, we cannot guarantee that this information includes all possible side effects. This information is not a substitute for medical advice. Always discuss possible side effects with a healthcare provider who knows your medical history.
SECTION 3 of 5

ampicillin May Interact with Other Medications

Oral capsule

Ampicillin can interact with other medications, vitamins, or herbs you may be taking. An interaction is when a substance changes the way a drug works. This can be harmful or prevent the drug from working well.

To help avoid interactions, your doctor should manage all of your medications carefully. Be sure to tell your doctor about all medications, vitamins, or herbs you’re taking. To find out how this drug might interact with something else you’re taking, talk to your doctor or pharmacist.

Medications that might interact with this drug

Interactions that increase your risk of side effects

Increased side effects from ampicillin: Taking ampicillin with certain medications raises your risk of side effects from ampicillin. This is because the amount of ampicillin in your body may be increased. Examples of these drugs include:

  • Probenecid
    • Taking this drug with ampicillin can cause more side effects. These can include severe nausea, vomiting, and diarrhea.
  • Allopurinol
    • This drug increases the risk of skin rash when you take it with ampicillin.

Interactions that can make your drugs less effective

When ampicillin is less effective: When you take ampicillin with certain drugs, it may not work as well to treat your condition. This is because the amount of ampicillin in your body may be decreased. Examples of these drugs include:

  • Antibiotics such as chloramphenicol, macrolides, sulfonamides, and tetracyclines
    • Your doctor may increase your ampicillin dosage or decrease the dosage of your other antibiotic if you need to take them together.

When other drugs are less effective: When certain drugs are used with ampicillin, they may not work as well. This is because the amount of these drugs in your body may be decreased. Examples include:

  • Oral contraceptives (birth control pills)
    • Your doctor may prescribe a different form of birth control for you.

Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs interact differently in each person, we cannot guarantee that this information includes all possible interactions. This information is not a substitute for medical advice. Always speak with your healthcare provider about possible interactions with all prescription drugs, vitamins, herbs and supplements, and over-the-counter drugs that you are taking.
Ampicillin warnings
gonorrhea and syphilis warning
People with gonorrhea and syphilis

This drug alone won’t treat syphilis. You must receive an injectable dose of penicillin if you have gonorrhea and syphilis.

diabetes warning
People with diabetes

This drug may cause a false positive when your doctor tests you for glucose (sugar) in your urine. That means the test may say you have glucose in your urine when you really don’t. Ask your doctor if this drug is safe for you.

kidney problem warning
People with kidney problems

If you have kidney problems or a history of kidney disease, you may not be able to clear this drug from your body well. This may increase the levels of drug in your body and cause more side effects.

pregnancy warning
Pregnant women

Ampicillin is a category B pregnancy drug. That means two things:

  1. Research in animals has not shown a risk to the fetus when the mother takes the drug.
  2. There aren’t enough studies done in humans to show if the drug poses a risk to the fetus.

Talk to your doctor if you’re pregnant or planning to become pregnant. Animal studies do not always predict the way humans would respond. Therefore, this drug should only be used in pregnancy if clearly needed.

breast feeding warning
Women who are breast-feeding

Ampicillin may pass into breast milk and cause side effects in a child who is breastfed. Talk to your doctor if you breastfeed your child. You may need to decide whether to stop breastfeeding or stop taking this medication.

senior warning
For seniors

The kidneys of older adults may not work as well as they used to. This can cause your body to process drugs more slowly. As a result, more of a drug stays in your body for a longer time. This raises your risk of side effects.

childrens warning
For children

Newborns and infants should take the lowest dosage of this drug possible. This is because their kidneys aren’t fully developed. It may take longer for this drug to be removed from their bodies. This means it can cause more side effects.

call the doctor
When to call the doctor

Call your doctor right away if you become pregnant while taking this drug.

allergy warning
Allergies

Ampicillin can cause a severe allergic reaction. Symptoms can include:

  • rash
  • trouble breathing
  • swelling of your throat or tongue

If you have an allergic reaction, call your doctor or local poison control center right away. If your symptoms are severe, call 911 or go to the nearest emergency room. Do not take this drug again if you’ve ever had an allergic reaction to it. Taking it again could be fatal.

SECTION 4 of 5

How to Take ampicillin (Dosage)

Oral capsule

All possible dosages and drug forms may not be included here. Your dosage, drug form, and how often you take the drug will depend on:

  • your age
  • the condition being treated
  • how severe your condition is
  • other medical conditions you have
  • how you react to the first dose

The dosage information below is for the conditions that this drug is most often prescribed to treat. This list may not contain all conditions that your doctor can prescribe this drug for. If you have questions about your prescription, talk with your doctor.

What are you taking this medication for?

Genitourinary tract infections, gonorrhea

Generic: Ampicillin

Form: oral capsule
Strengths: 250 mg, 500 mg
Form: suspension
Strengths: 125 mg/5 mL, 250 mg/5 mL
Adult dosage (ages 18–64 years)

For gonorrhea:

  • 3.5 grams as a single dose

For genitourinary tract infections other than gonorrhea:

  • 500 mg four times per day
Child dosage (children who weigh 20kg or more)

For genitourinary tract infections other than gonorrhea:

  • 500 mg four times per day

For gonorrhea:

  • 3.5 grams as a single dose
Child dosage (children who weigh less than 20kg)

For genitourinary tract infections:

  • 100 mg/kg per day in four equally divided and spaced doses
Senior dosage (ages 65 years and older)

The kidneys of older adults may not work as well as they used to. This can cause your body to process drugs more slowly. As a result, more of a drug stays in your body for a longer time. This raises your risk of side effects.

Your doctor may start you on a lowered dosage or a different schedule. This can help keep levels of this drug from building up too much in your body.

Respiratory tract infections

Generic: Ampicillin

Form: oral capsule
Strengths: 250 mg, 500 mg
Form: suspension
Strengths: 125 mg/5 mL, 250 mg/5 mL
Adult dosage (ages 18–64 years)
  • 250 mg four times per day
Child dosage (children who weigh 20kg or more)
  • 250 mg four times per day
Child dosage (children who weigh less than 20kg)
  • 50 mg/kg per day in equally divided and spaced doses three to four times per day
Senior dosage (ages 65 years and older)

The kidneys of older adults may not work as well as they used to. This can cause your body to process drugs more slowly. As a result, more of a drug stays in your body for a longer time. This raises your risk of side effects.

Your doctor may start you on a lowered dosage or a different schedule. This can help keep levels of this drug from building up too much in your body.

Gastrointestinal tract infections

Generic: Ampicillin

Form: oral capsule
Strengths: 250 mg, 500 mg
Form: suspension
Strengths: 125 mg/5 mL, 250 mg/5 mL
Adult dosage (ages 18–64 years)
  • 500 mg four times per day
Child dosage (children who weigh 20kg or more)
  • 500 mg four times per day
Child dosage (children who weigh less than 20kg)
  • 100 mg/kg per day in four equally divided and spaced doses
Senior dosage (ages 65 years and older)

The kidneys of older adults may not work as well as they used to. This can cause your body to process drugs more slowly. As a result, more of a drug stays in your body for a longer time. This raises your risk of side effects.

Your doctor may start you on a lowered dosage or a different schedule. This can help keep levels of this drug from building up too much in your body.

Meningitis

Generic: Ampicillin

Form: oral capsule
Strengths: 250 mg, 500 mg
Form: suspension
Strengths: 125 mg/5 mL, 250 mg/5 mL
Adult dosage (ages 18–64 years)

Your doctor will decide the dosage that’s right for you

Child dosage (ages 0–17 years)

Your child’s doctor will decide the dosage that’s right for your child.

Senior dosage (ages 65 years and older)

The kidneys of older adults may not work as well as they used to. This can cause your body to process drugs more slowly. As a result, more of a drug stays in your body for a longer time. This raises your risk of side effects.

Your doctor may start you on a lowered dosage or a different schedule. This can help keep levels of this drug from building up too much in your body.

Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs affect each person differently, we cannot guarantee that this list includes all possible dosages. This information is not a substitute for medical advice. Always to speak with your doctor or pharmacist about dosages that are right for you.
Pharmacist's Advice
Healthline Pharmacist Editorial Team

Ampicillin comes with serious risks if you don’t take it as prescribed.

If you stop taking the drug suddenly or don’t take it at all

Your bacterial infection may not get better. It may even get worse.

If you miss doses or don’t take the drug on schedule

Your medication may not work as well or may stop working completely. For this drug to work well, a certain amount needs to be in your body at all times.

Finish all of your medication that your doctor prescribes. Don’t stop taking your drug or skip doses if you start to feel better. Doing so could make your infection last longer. You could also become resistant to the drug. This means that if you get another bacterial infection, ampicillin may not work to treat it.

If you take too much

You could have dangerous levels of the drug in your body. Symptoms of an overdose of this drug can include:

  • upset stomach
  • diarrhea

If you think you’ve taken too much of this drug, call your doctor or local poison control center. If your symptoms are severe, call 911 or go to the nearest emergency room right away.

What to do if you miss a dose

Take your dose as soon as you remember. But if you remember just a few hours before your next scheduled dose, take only one dose. Never try to catch up by taking two doses at once. This could result in dangerous side effects.

How to tell if the drug is working

The symptoms of your infection will get better.

Ampicillin is used for short-term treatment.

Don’t take this drug with food

Take it with 8 oz. of water a half hour before eating or two hours after eating.

Store this drug carefully

  • Store the capsules at room temperature between 68°F and 77°F (20°C and 25°C).
  • Store the capsules away from light.
  • Store the mixed suspension in the refrigerator. Don’t freeze it.
  • Throw away any unused suspension after 14 days.

A prescription for this medication is refillable

You should not need a new prescription to refill this medication. Your doctor will write the number of refills authorized on your prescription.

Travel

When traveling with your medication:

  • Always carry your medication with you. When flying, never put it into a checked bag. Keep it in your carry-on bag.
  • Don’t worry about airport x-ray machines. They can’t hurt your medication.
  • You may need to show airport staff the pharmacy label for your medication. Always carry the original prescription-labeled box with you.
  • Don’t put this medication in your car’s glove compartment or leave it in the car. Be sure to avoid doing this when the weather is very hot or very cold.

Self-management

If you’re taking the oral suspension, make sure to shake well before each use. You should also use a specially marked spoon or container to measure the correct dose. Your pharmacist may be able to give you one. Do not use a normal household spoon. You may get too much or too little medication.

Clinical monitoring

You and your doctor should monitor certain health issues during your treatment. This can help make sure you stay safe while you take this drug. These issues include:

  • Kidney function. Your doctor may do blood tests to check how well your kidneys are working. If your kidneys don’t work well, your doctor may reduce how often you take this drug.
  • Liver function. Your doctor may do blood tests to check how well your liver is working. If your liver doesn’t work well, your doctor may lower your dosage of this drug.
  • Blood cell counts. Your doctor may do blood tests to check if this drug is reducing your red blood cell and platelet levels. If it is, your doctor may lower your dosage or your stop treatment with the drug.
  • Syphilis. If you have gonorrhea, your doctor will also test for you for syphilis. They’ll do this when you start the drug and then again three months later. This is because treatment for gonorrhea can mask symptoms of syphilis.

Are there any alternatives?

There are other drugs available to treat your condition. Some may be better suited for you than others. Talk to your doctor about other drug options that may work for you.

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How Much Does ampicillin Cost?

Oral capsule

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Lowest price for ampicillin

Walmart $11.79
Sams Club $11.79
Kroger Pharmacy $13.75
These prices represent the lowest priced national pharmacies for ampicillin on GoodRx. They may be lower than your insurance.

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These prices represent the lowest priced national pharmacies for ampicillin on GoodRx. They may be lower than your insurance.

Show Sources

Content developed in collaboration with University of Illinois-Chicago, Drug Information Group

Medically reviewed by Creighton University, Center for Drug Information and Evidence-Based Practice on May 27, 2016

Disclaimer: Healthline has made every effort to make certain that all information is factually correct, comprehensive, and up-to-date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or other healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.
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