Amoxicillin: uses, dosing, side effects and penicillin allergy

Amoxicillin is an antibiotic in the penicillin family. According to MedlinePlus, it works by stopping the growth of the bacteria that cause the infection. It comes as capsules, tablets, chewable tablets and an oral liquid (suspension), and it is one of the most commonly prescribed antibiotics, especially for children.

There is a combination, amoxicillin with clavulanate (brand name Augmentin), that adds an ingredient protecting amoxicillin from bacteria that break it down. It is used for some infections where amoxicillin alone is not enough. This guide covers amoxicillin in general; for other antibiotics, read antibiotics by telehealth.

According to MedlinePlus, the FDA label published on DailyMed and the CDC, amoxicillin is used for infections caused by bacteria, such as:

No. In the United States and Puerto Rico, amoxicillin is a prescription medicine: pharmacies do not sell it over the counter. Pills offered "without a prescription" in informal shops, on social media or online come with no guarantee of what they contain or how much, and taking the wrong or an incomplete antibiotic can mask the infection, trigger an allergic reaction or make bacteria more resistant.

Leftovers from an earlier course are not a good idea either. Every infection needs its own evaluation: many illnesses that look like infections (colds, flu, most bronchitis and many sore throats) are viral, and according to the CDC antibiotics do not cure them. What you can do is get evaluated: the doctor reviews your symptoms, allergies and medicines and decides whether an antibiotic is right for you.

The dose is not the same for everyone. The doctor decides it based on the type of infection, your age, your weight and how well your kidneys work; that is why this guide gives no amounts and you should not copy another person's dose or one from an old bottle. For children, the dose is calculated by weight and measured with an oral syringe or dosing spoon, not a kitchen spoon.

Here is what MedlinePlus and the FDA label say about taking it:

• You can take it with or without food. If it upsets your stomach, take it with food.
• Chew chewable tablets thoroughly, and shake the liquid suspension before measuring.
• Finish the whole course your doctor prescribed, even if you feel better after a few days, unless the doctor tells you otherwise.
• If you miss a dose, take it when you remember; if it is almost time for the next one, skip the missed dose. Do not double up.
• If you are not better in 2 to 3 days, or you get worse, check back in: the infection may not be bacterial, or you may need a different plan.

The most common effects listed by MedlinePlus and the FDA label are upset stomach, nausea, vomiting, mild diarrhea and rash. They are usually mild. Taking the medicine with food and drinking enough fluids helps. Antibiotics can also cause yeast infections, such as thrush in the mouth or a vaginal yeast infection.

These effects are more serious and need medical attention:

• Severe, watery or bloody diarrhea, or stomach cramps. Antibiotics can allow an intestinal infection with *C. difficile*, and MedlinePlus warns it can show up more than two months after finishing treatment. Do not take anti-diarrhea medicine without asking.
• Hives, itching, swelling of the face, lips or tongue, or trouble breathing: signs of an allergic reaction (see below).
• Skin that blisters or peels, or mouth sores.
• Yellow skin or eyes or dark urine, which can point to a liver problem.
• Unusual bruising or bleeding.

Penicillin allergy is the most important precaution with amoxicillin, because they are in the same family. If you have ever had a reaction to penicillin, amoxicillin or a cephalosporin, tell the doctor before any antibiotic is decided on. Also say what the reaction was, how long ago, and how old you were.

An allergic reaction to amoxicillin can appear within minutes or hours and often includes hives or itching all over, swelling of the face, lips, tongue or throat, wheezing, shortness of breath, dizziness or fainting. That is an emergency: call [911](tel:911). See when to go to the ER.

A useful point from the CDC: about 1 in 10 people say they are allergic to penicillin, but the large majority of them, when evaluated, are not (for example, a childhood rash or stomach upset is not an allergy). A wrong allergy label in your chart limits your antibiotic options. If you are not sure what happened to you, tell the doctor: she decides whether to avoid penicillin or whether an allergy evaluation with a specialist makes sense. Do not test it on yourself "to see what happens."

One more detail: according to the FDA label, people with mononucleosis ("mono") who take amoxicillin often develop a rash that is not a true allergy but is confusing. That is why antibiotics in this family are avoided when mono is suspected.

Before starting, tell the doctor and the pharmacist everything you take, including supplements. According to MedlinePlus and the FDA label, these are the most important precautions:

Amoxicillin kills bacteria; it does nothing against viruses. Colds, the flu, most bronchitis and many sore throats are caused by viruses. Taking it "just in case" does not cure you faster and does expose you to side effects and to antibiotic resistance: when antibiotics are used unnecessarily, bacteria learn to survive them, and when you truly need one it may not work.

Signs that suggest a bacterial infection worth evaluating: a high fever lasting more than a few days or one that improves and then returns, a severe sore throat without cough and with swollen glands, face or sinus pain that lasts past 10 days without improving, ear pain with fever, a red, warm, increasingly painful wound, or burning with urination. The doctor asks questions and, if needed, orders a test before deciding. If it is not a bacterial infection, she explains how to ease the symptoms.

If you are taking amoxicillin or think you have an infection and notice any of these signs, call 911 or go to the emergency room. See when to go to the ER.