Amoxicillin side effects and how to avoid them

Amoxicillin side effects | Hypersensitivity | Superinfections | Clostridium difficile | How long do side effects last? | Warnings | Interactions | How to avoid side effects

Amoxicillin is a generic antibiotic that treats a wide range of bacterial infections: upper respiratory tract infections such as sinusitis, lung infections such as bronchitis or pneumonia, skin infections, middle ear infections, urinary tract infections, as well as H. pylori stomach infections. 

Also prescribed under the brand names Amoxil and Augmentin (amoxicillin/clavulanate), amoxicillin is a penicillin antibiotic that kills bacteria by blocking their ability to make and repair their protective cell walls. For most infections, amoxicillin will only be given for a few days. Many people taking amoxicillin will experience minor side effects, but serious side effects, and drug interactions with existing medical conditions are also possible.

RELATED: What is amoxicillin?

Common side effects of amoxicillin

The most common side effects of amoxicillin are temporary and manageable. These include:

• Rash
• Diarrhea
• Headache
• Nausea
• Vomiting
• Stomach pain
• Tongue discoloration
• Yeast infection
• Elevated liver enzymes
• High white blood cell counts (eosinophilia)

Serious side effects of amoxicillin

Serious but less common side effects of amoxicillin include:

• Superinfections
• Clostridium difficile-associated diarrhea
• Liver problems such as swelling (hepatitis) and obstructive jaundice (cholestatic jaundice)
• Blood disorders such as hemolytic anemia (rapid red blood cell death), low platelets, or agranulocytosis (low counts of a certain type of white blood cell)
• Seizures 
• Swelling of the brain and spinal cord membranes (aseptic meningitis)
• Severe allergic reactions

Amoxicillin and hypersensitivity

Allergies to penicillin antibiotics such as amoxicillin and ampicillin are very common and potentially hazardous. About one in 10 people report a penicillin allergy. However, many people mistake drug side effects such as GI upset for an allergy. And even among patients with an actual hypersensitivity reaction, most are mild reactions, usually a delayed skin rash. These symptoms are less concerning than the immediate, life-threatening symptoms of anaphylaxis. Only 0.02% to 0.04% of the population experience a true allergy to amoxicillin that results in anaphylaxis. 

At one time, any person reporting an allergic reaction to penicillins or similar drugs such as cephalosporin antibiotics would not be given amoxicillin. Healthcare providers are still cautious about giving amoxicillin or any other penicillin drug to any person who has had a past reaction to amoxicillin or similar drugs. However, healthcare professionals now know that at least 90% of people who report penicillin allergy do not have a true allergy. In addition, people who have had a true allergic reaction tend to lose their sensitivity over time. 

As a result, people with a history of low-level reactions to penicillins may be administered a skin test to determine the exact nature of the allergy. Some of these patients can be given amoxicillin safely, but the treatment will require monitoring. However, amoxicillin will not be given to any person with a history of a serious hypersensitivity reaction to penicillins such as anaphylaxis.

Amoxicillin and superinfections

Bacteria normally limit the growth of other microorganisms in the body. Nearly all antibiotics, however, kill off native bacteria colonies, allowing other microorganisms to grow out of control, called superinfections. For amoxicillin, the most common superinfections are fungal infections of the mouth or vagina and overgrowth of Clostridium difficile in the colon. The incidence of C. difficile overgrowth is unknown, but about 2% of people taking amoxicillin will experience a yeast infection.

Amoxicillin and Clostridium difficile

Nearly all antibiotics alter the microorganism environment of the colon, allowing an overgrowth of C. difficile bacteria colonies that are normally kept low by other bacteria in the colon. C. difficile-associated diarrhea, or CDAD, is a common and potentially serious side effect of amoxicillin therapy, occurring in 5% of people taking drugs like amoxicillin. In mild cases, CDAD can cause little more than mild diarrhea. In severe cases, bacterial overgrowth can lead to potentially fatal swelling of the colon. 

As a side effect, C. difficile-associated diarrhea can occur during amoxicillin treatment or as much as two months after treatment has ended. If diarrhea occurs during or after any antibiotic treatment, talk to a healthcare provider. If the diarrhea is watery or bloody, get immediate medical attention.

How long do Amoxicillin side effects last?

Amoxicillin is only given for a few days. Most side effects are temporary and will fade when treatment ends. Some amoxicillin side effects, however, are delayed and may take longer to resolve, such as allergic reactions and blood disorders. Clostridium difficile infection can be delayed for up to two months after amoxicillin treatment has stopped. Some side effects may require medical treatment such as yeast infections, allergic reactions, blood problems, superinfections, or C. difficile infection.

Amoxicillin contraindications & warnings

Amoxicillin won’t be given to everyone. Some people will not be able to take amoxicillin at all, while others may require dose adjustments or monitoring.

Abuse and dependence

Amoxicillin and similar antibiotics are not commonly abused or used recreationally. They are prescribed for only a short duration and do not cause physical dependence or withdrawal symptoms.

Overdose

Amoxicillin should only be taken as prescribed for the duration prescribed. Taking too much amoxicillin can result in unpleasant side effects such as upset stomach and diarrhea, but usually does not cause serious problems. However, in rare cases, an amoxicillin overdose can damage the kidneys or result in renal failure. If an amoxicillin overdose is suspected, immediately call a poison control center.

Restrictions

Although amoxicillin is widely used, some people may not be able to take the drug. Others may require lower doses or careful monitoring.

People who have a history of severe anaphylactic allergic reactions to penicillins or similar drugs—called beta-lactam antibiotics—will not be given amoxicillin. Amoxicillin may, however, be given to people with a history of very mild allergies to beta-lactams, but they will need to take a skin test first. If the healthcare provider determines that they can safely take amoxicillin, they will be monitored carefully for allergic reactions. People with multiple allergies or asthma will also need to be tested and monitored. An allergic reaction (drug rash) is also possible when amoxicillin is given to people with mononucleosis, so healthcare providers will most likely use another antibiotic.

Most antibacterial drugs increase the risk of pseudomembranous colitis, so any patient with colitis, inflammatory bowel disease (IBD), or diarrhea will require monitoring while on amoxicillin therapy. Other medical conditions that also require heightened monitoring or dose adjustment include kidney disease, HIV infection, acute lymphocytic leukemia, and epilepsy. 

Pregnancy and nursing

There is no evidence that amoxicillin will harm a fetus, but healthcare providers are not certain amoxicillin is safe to take during pregnancy. Women should talk to a healthcare provider about possible risks before taking amoxicillin. 

Amoxicillin and similar drugs are present in breast milk. While there is no evidence that amoxicillin will harm a breastfeeding baby, healthcare providers are cautious. Because the infant may develop allergies to the drug, a healthcare provider may choose a different antibiotic or encourage the mother to temporarily stop nursing the infant.

Children

The Food and Drug Administration (FDA) has approved the use of amoxicillin in children as young as newborns. Doses will be reduced in infants younger than 12 weeks old.

Seniors

Amoxicillin is routinely prescribed to people older than65, and there is no evidence that its use is less effective or less safe than in younger people. Doses may be reduced if a healthcare provider has worries about the person’s kidney function.

Amoxicillin interactions

While Amoxicillin has several minor drug interactions, a few prescription drugs will cause problems when combined with amoxicillin. 

• Oral contraceptives. Amoxicillin may reduce the effectiveness of oral contraceptives, though there is some disagreement in the research. Still, women on birth control are advised to use backup birth control when taking amoxicillin.
• Tetracyclines. Antibiotics such as doxycycline are generally avoided in combination with penicillins. These drugs, called tetracyclines, reduce the effectiveness of amoxicillin.
• Live vaccines. Live, weakened bacteria vaccines such as BCG or typhoid vaccine are less effective when given to a person taking amoxicillin. The bacteria are killed off before they can elicit a strong antibody response. 
• Warfarin. Close monitoring is required when combining amoxicillin with warfarin. Many types of antibiotics, including amoxicillin, reduce the body’s ability to form blood clots when combined with warfarin, a blood-thinning drug. Other blood thinners, however, are safe to take with amoxicillin.

• Allopurinol. An allergic reaction to amoxicillin is more likely when it is combined with the gout medication, allopurinol. In some cases, allopurinol has even precipitated severe allergic reactions to amoxicillin.

Some amoxicillin drug interactions are beneficial. The gout medication, probenecid, increases the effectiveness of amoxicillin. Some people without gout may be prescribed both drugs to treat certain types of infections. The effectiveness of amoxicillin is also enhanced by aminoglycoside antibiotics.

How to avoid amoxicillin side effects

Side effects are common when taking amoxicillin or any other penicillin antibiotic. A few tips can help minimize side effects or ensure the maximum benefit from the drug.

1. Tell your healthcare provider about all medical conditions and medications

Start by informing the healthcare provider prescribing amoxicillin about all past and present medical conditions, especially:

• Kidney problems
• Drug allergies or reactions to antibiotics
• Mononucleosis
• Any history of diarrhea when taking antibiotics
• Gastrointestinal problems

Some problems may arise when amoxicillin is combined with other drugs, but these drug interactions are uncommon. Always give the healthcare provider a complete list of all prescription and nonprescription medications being taken, especially birth control pills, antibiotics, or drugs that require precise dose adjustments such as methotrexate, or warfarin.

2. Take amoxicillin as directed

Take this drug as directed. Don’t miss a dose. If you do miss a dose, take it as soon as you remember unless it is almost time for your next dose. Don’t take extra medicine to make up for a missed dose. Above all, take the medicine for the full duration of the prescription. Even if symptoms go away, it’s important to take the medication for the entire duration to ensure the bacterial infection is wiped out. If you have any questions about when or how to take your medicine, call your local pharmacy.

3. Do not use amoxicillin for other infections

Amoxicillin is effective against some bacterial infections but will not help eradicate other bacterial or viral infections. To avoid unnecessary side effects, only take amoxicillin for the bacterial infection indicated. If any medicine is left over, don’t save it. Ask a pharmacist how to safely dispose of unused amoxicillin.

4. Take amoxicillin as scheduled

To successfully eradicate a bacterial infection, amoxicillin is intended to be taken frequently so that its concentration in the body stays high. The goal is to continually kill bacteria without any let-up. Late or missed doses allow the bacteria to start growing again and increase the risk of the infection evolving into a drug-resistant form. Make sure that each dose is taken on time. Amoxicillin may also be prescribed with other drugs, such as clarithromycin or lansoprazole, for certain infections. It is important to take all prescribed drugs on schedule. If there’s a problem with late or missed doses, a pharmacist can suggest alarms, apps, and other tools to make sure doses are remembered on time. 

5. Take amoxicillin with food

Amoxicillin can usually be taken with a meal or on an empty stomach. Unless instructed otherwise, take amoxicillin with food to avoid side effects such as nausea, vomiting, stomach cramps, and abdominal pain.

6. Watch for signs of an allergic reaction

Allergic reactions are among the most common side effects of amoxicillin and other penicillin antibiotics. Most are mild reactions, but they should be taken seriously. Watch for signs of an allergic reaction, such as:

• Skin rash
• Hives
• Swelling

Get medical advice if any allergic reaction is noticeable. Get emergency medical help at any sign of trouble breathing, wheezing, lightheadedness, clammy skin, confusion, fever, sore throat, skin pain, or blistering.

7. Watch for diarrhea

Diarrhea is another common side effect of amoxicillin. This is usually okay and can be treated with over-the-counter anti-diarrheal medications. Diarrhea may, however, be a sign of a more serious problem if the diarrhea is watery or bloody. If this happens, immediately see a healthcare provider rather than treat the diarrhea on your own.

Related resources for amoxicillin side effects:

• Amoxicillin, Epocrates
• Amoxicillin, StatPearls
• Amoxicillin capsules, oral suspension, chewable tablets prescribing information, U.S. National Library of Medicine
• Amoxicillin drug summary, Prescriber’s Digital Reference
• Clostridium difficile-associated diarrhea in patients with community-acquired lower respiratory infection being treated with levofloxacin compared with beta-lactam-based therapy, Clinical Trial
• Hypersensitivity to amoxicillin after drug rash with eosinophilia and systemic symptoms (DRESS) to carbamazepine and allopurinol: a possible co-sensitization, British Journal of Clinical Pharmacology
• Penicillin allergy, StatPearls
• Prevalence and characteristics of reported penicillin allergy in an urban outpatient adult population, Allergy and Asthma
• Probenecid, LiverTox