How Long Does Amoxicillin Stay in Your System?

By Terez Malka, MD
Medically reviewed checkmarkMedically reviewed
December 14, 2021

When you take antibiotics for a bacterial infection, the medicine can stay in your body for hours or even days after you take them.

Amoxicillin, one of the most commonly prescribed antibiotics, is removed from your body faster.

The amount in your body is often significantly decreased within 5-7 hours.

In this article, I’ll tell you more about how amoxicillin works, what it’s used for, and the side effects it can cause.

I’ll then explain more about how long it lasts in your body.

Finally, I’ll tell you when to talk to a doctor or healthcare professional.

What is Amoxicillin?

Amoxicillin is an antibiotic that is prescribed 50 million times per year in the United States.

It is penicillin-like, because it is made by pairing an extra amino group with penicillin.

This helps combat resistance to the drug

Amoxicillin works by inhibiting bacterial growth.

Like other antibiotics, amoxicillin will not work to treat viruses.

It is sometimes used to address bacterial complications associated with viral infections, like bacterial pneumonia or atypical pneumonia after a cold or flu virus.

Patients who are allergic to penicillin may also be allergic to amoxicillin.

Keep your doctor informed about allergies or side effects that you experience from any medications.

Uses

Bacterial infections occur when specific types of pathogenic (disease-causing) bacteria get into the body and multiply.

You can encounter these in the same ways you would viral infections, from exposure to other people, contaminated food, or commonly shared surfaces.

In some cases, bacterial infections can happen as a result of an imbalance with bacteria that naturally lives in the body or on the surface of the skin (like urinary tract infections or acne).

Amoxicillin is used to treat a wide range of bacterial infections and medical conditions in adults and children:

Side Effects

Common side effects of amoxicillin:

These are typically mild. If your doctor has prescribed amoxicillin for you, they have decided that the benefits outweigh the side effects.

However, if you notice that any symptoms worsen or you have concerns, you should check in with your healthcare provider.

Be sure your doctor is aware of your medical history, allergies, and the other medications that you take, including birth control.

More serious side effects are possible but less common.

If you notice these symptoms, stop taking your medicine and contact your doctor immediately or seek emergency medical care. 

Seek immediate medical attention if you experience the following:

  • Itching, hives, or skin rashes
  • Wheezing or difficulty breathing
  • Skin blisters
  • Swelling of the lips, face, throat, tongue, or eyes
  • Stomach cramps
  • Severe diarrhea, watery diarrhea, or bloody stools

This list of possible side effects is not exhaustive.

Other reactions may be possible.

If you have questions or concerns about your amoxicillin, ask your doctor or pharmacist.

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How Long Amoxicillin Lasts in The Body

It only takes a little over an hour for the dose of amoxicillin in your body to be reduced by half.

This is called the medicine’s “half-life,” and it’s shorter than other antibiotics.

Amoxicillin is primarily excreted via the kidneys and urine.

Within 8 hours of taking the drug, 60% of it has already been passed from the body.

Because elimination of amoxicillin primarily happens via the kidneys, it may last longer or need to be dosed differently in those who  have kidney disease, so make sure to mention that to your prescriber

After your last dose of amoxicillin, you can expect that it will be mostly gone from your body within 8 hours.

After 12 hours, there should be none left in your system.

This is one reason it’s important to take your medication as prescribed.

If you cut your course of antibiotics short, within 8-12 hours the bacteria causing your infection could start to ramp up again.

This can contribute to the development of drug-resistant bacteria and more severe infection. 

Your antibiotic prescription is designed to effectively address the bacteria completely before the drug is out of your body.

This is why dosage and the number of days you will take amoxicillin are important.

Take the medication as prescribed, and don’t stop until your course is complete or your doctor says to stop.

If you have leftover medication at the end of your course of treatment, discard it.

Do not flush it down the toilet.

Amoxicillin also expires quickly. Use of amoxicillin after 14 days is unsafe- check your package expiration date or ask your pharmacist if you are unsure

When to See a Doctor

If you have questions about a sickness that seems to be lasting longer than you would expect, seek medical advice from your doctor.

If you are taking amoxicillin for an infection and are not better when your medication is done, let your doctor know.

How K Health Can Help

Have questions about amoxicillin, whether it could help you, or things you need to know about a current prescription?

You can speak to a primary care doctor from the comfort of your own home with K Health.

You can get affordable primary care with the K Health app.

Download K to check your symptoms, explore conditions and treatments, and if needed text with a doctor in minutes. K Health’s AI-powered app is HIPAA compliant and based on 20 years of clinical data.

Frequently Asked Questions

Will antibiotics continue to work after you stop taking them?
Yes, antibiotics continue their antibacterial effects after your last dose. Some will last in the body longer than others. While doxycycline may take several days to clear, amoxicillin is excreted from the body more quickly. It will be nearly undetectable after 8 hours.
What is the most common side effect of amoxicillin?
The most common side effect of amoxicillin is digestive upset, like nausea or vomiting. These symptoms are common to many antibiotics and should be mild. If you feel concerned that your symptoms are worsening, let your healthcare provider know right away.
How long will it take for side effects from amoxicillin to go away?
The side effects of amoxicillin will resolve when you are done taking the medication. Your body clears the medication quickly, typically within 8-12 hours of your last dose.

K Health articles are all written and reviewed by MDs, PhDs, NPs, or PharmDs and are for informational purposes only. This information does not constitute and should not be relied on for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment.

Terez Malka, MD

Dr. Terez Malka is a board-certified pediatrician and emergency medicine physician.