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Common Amoxicillin Drug Interactions

Amoxicillin is a widely prescribed, penicillin-based antibiotic for treating bacterial infections. However, other medications can negate amoxicillin’s healing ability and create negative side effects. Everyday painkillers such as aspirin, ibuprofen and Tylenol do not mix well with amoxicillin.

Last Modified: August 19, 2022
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How Does Amoxicillin Interact with Common Drugs?

Amoxicillin interacts with several everyday drugs and supplements, all of which should be listed on amoxicillin’s label. Most interactions are classed as mild or moderate, but there are a few that may cause severe symptoms.

Give your doctor a list of any drugs, vitamins and supplements you are taking when you receive a prescription for amoxicillin.

This is especially true if you take any of the following medications:
  • Allopurinol (Lopurin, Zyloprim)
  • Blood thinners such as warfarin (Coumadin, Jantoven)
  • Oral contraceptive medications
  • Probenecid (Probalan)
  • Other antibiotics

If you take any of these medications, your doctor may need to lower your dose of them temporarily or monitor you closely for potential side effects once you start taking amoxicillin.

Tylenol, Ibuprofen (Advil) and Aspirin

Common painkillers like Tylenol, ibuprofen and aspirin also have potential side effects that overlap with those of amoxicillin. For example, drugs like amiodarone, furosemide and paracetamol (acetaminophen or Tylenol) significantly increase the risk of gingival bleeding when taken with amoxicillin.

None of these side effects are serious, but you may find it worthwhile to switch to a different type of painkiller if you experience any unpleasant reactions.

Some evidence also suggests that taking aspirin and amoxicillin together can alter your gut bacteria levels. The combination may make the aspirin less effective and cause more significant side effects. Scientists would like to see more research data to confirm the interactions and document their effects, but for now they advise against mixing aspirin and amoxicillin.

However, they say it is safe to use any other over-the-counter pain medication for pain or fever relief while taking amoxicillin. Let your doctors know what medications (and dosages) you take and alert them if your symptoms get worse while taking them with amoxicillin. Any adverse reaction could be a sign that amoxicillin’s healing effects are being negated and that your bacterial infection is getting worse.

Oral Birth Control

Amoxicillin does not interact with any form of oral birth control. When you start taking amoxicillin, you may receive warning documentation that states that the drug can alter the effectiveness of your birth control. This information is outdated, and current evidence-based guidelines do not support this conclusion.

The effectiveness of your oral birth control will not change while you are taking amoxicillin. You do not need to use a back-up method of birth control during this period.

Continue taking your usual dose of oral contraceptives at the correct time to keep them working as intended.

Possible Serious Amoxicillin Drug Interactions

While many medications can be taken at the same time as amoxicillin safely, there are several medications that can have potentially serious negative outcomes when taken with amoxicillin. These include anticoagulants, the live typhoid vaccine, allopurinol, probenecid and methotrexate, which is an antimetabolite.

Methotrexate is often prescribed for patients with certain forms of cancer, like breast cancer and leukemia, multiple sclerosis, psoriasis, Crohn’s disease, rheumatoid arthritis and severe psoriasis. Anticoagulants are blood thinners prescribed to help prevent blood clots from forming and are often prescribed to patients at risk of clotting following surgery. Probenecid and allopurinol are both used to treat gout.

Typhoid vaccines are not routinely recommended for patients in the U.S., but may be given to those planning overseas travel. Guar gum is derived from guar beans and is typically used as a thickening agent in some foods. It has gained popularity as a supplement, but this use is not regulated and research is needed to determine benefits and potential risks.

Anticoagulants

Amoxicillin can make it harder for your body to absorb anticoagulants like warfarin. This can amplify these drugs’ effects and even lead to dangerous secondary conditions like warfarin toxicity and internal bleeding.

Doctors sometimes prescribe warfarin and amoxicillin at the same time when treating severe infections. If this is deemed your best treatment option, your doctor should monitor you for symptoms of possible side effects.

But most people who take a short-term dose of amoxicillin while taking anticoagulants do not experience coagulation issues.

Always remind your doctor that you are taking anticoagulants when you receive a prescription for a new medication. Also ask about possible interactions between your drugs. This will help you get a better sense of the risks involved in your treatment.

Live Typhoid Vaccine

Getting a live typhoid vaccine while you are taking amoxicillin may decrease the vaccine’s effectiveness. That is because doctors employ antibiotics to treat typhoid infections.

Talk to your doctor or vaccine provider if you are scheduled to receive the live typhoid vaccine while taking or shortly after taking amoxicillin. They may recommend that you postpone your vaccination for a future visit to ensure you get as much protection from typhoid bacteria as possible.

Methotrexate

Pharmacists strongly recommend not taking penicillin and methotrexate. Penicillin interferes with your body’s ability to absorb the methotrexate, causing it to build up to abnormally high levels. This leads to unpleasant side effects and possible toxicity.

One exception is amoxicillin. Evidence suggests that amoxicillin is one of the few penicillin-based antibiotics that do not interfere with methotrexate absorption in the way that other penicillin drugs do.

Guar Gum

Early research indicates that guar gum may reduce the effectiveness of penicillin antibiotics like amoxicillin. Guar gum, fiber from the seed of the guar plant, absorbs excess moisture in the stool and cholesterol and glucose in the stomach and intestines. It helps treat diarrhea, irritable bowel syndrome (IBS), constipation, high blood pressure and high cholesterol.

Doctors recommend that people only take any supplements containing guar gum two hours before or after taking amoxicillin. Guar gum in food products also may have an effect, but more research is needed to make a recommendation either way.

Allopurinol

Allopurinol, a common generic gout medication, may make you more sensitive to amoxicillin when the two drugs are taken together. This makes you more likely to develop an allergic reaction to amoxicillin, especially a skin rash. Allopurinol is also known as Lopurin and Zyloprim.

Contact your doctor immediately if you experience any symptoms of an allergic reaction while taking these medications together.

Probenecid

Probenecid (also sold as Probalan and found in Col-Probenecid) has been proven to make it more difficult for the kidneys to filter antibiotics from the body. Doctors sometimes exploit this side effect to increase the effectiveness of penicillin medications like amoxicillin.

If you take probenecid for other reasons when you are prescribed amoxicillin, let your doctor know so your dose can be adjusted to compensate for these effects.

Symptoms of Dangerous Amoxicillin Interactions

Most possible interactions with amoxicillin are considered mild or moderate and not dangerous. Only a few interactions are potentially life-threatening.

Contact your doctor immediately if you experience any of the following while taking amoxicillin and a drug it is known to interact with:

  • A persistently high fever
  • Sudden sweats or chills
  • Unexplained fatigue
  • New or worsening pain
  • New or worsening gastrointestinal symptoms like nausea, vomiting and diarrhea
  • Skin rashes
  • Sudden weakness
  • Numbness or tingling in your hands and feet
  • Confusion and lightheadedness
  • Blood in your stool or urine

You may need emergency treatment to resolve the effects of the interaction.

Remember that severe drug interactions are rare when taking amoxicillin. Overall, the drug is very safe.

Amoxicillin Contraindications

Certain people should not take amoxicillin. This includes people who are allergic to:
  • Penicillin antibiotics
  • Cephalosporin antibiotics (such as cefaclor, cefadroxil, cefazolin and others)
  • Any of the other ingredients in amoxicillin capsules, powders or tablets

Always tell your doctor about your drug allergies when you receive a prescription for a new medication.

Also, people with certain illnesses should not take amoxicillin. Tell your doctor if you have:
  • Mononucleosis (“mono")
  • Kidney disease
  • Asthma
  • A history of allergies, hay fever or hives

People with phenylketonuria (PKU) can take amoxicillin in most forms. However, some tablets are sweetened with aspartame, an artificial sweetener that forms an amino acide called phenylalanine, which has shown to cause brain damage in people with PKU.

Amoxicillin can also have negative effects on developing fetuses and infants. Tell your doctor if you:
  • Are pregnant
  • Are trying to get pregnant
  • Get pregnant while taking amoxicillin
  • Are breastfeeding
Please seek the advice of a medical professional before making health care decisions.