Amoxicillin: what is it and how does it work?

Amoxicillin: what is it and how does it work?

Amoxicillin is a penicillin used for for fighting bacterial infection.

Amoxicillin is a widely-used antibiotic drug. It belongs to the penicillin group of drugs and is prescribed to treat certain infections that are caused by bacteria.

It can also be used alongside other medications to treat stomach ulcers caused by H. pylori infection.

In the United States (U.S.), its brand names include Larotid, Amoxil, DisperMox, Moxilin, and Trimox.

Here are some key points about amoxicillin. More information is in the main article.

  • Amoxicillin works by preventing bacteria from growing, and killing them.
  • Amoxicillin can treat infections caused by bacteria but not those caused by viruses.
  • It can be used with other medications to treat some stomach ulcers.
  • Common adverse effects include diarrhea, candidiasis, and tooth discoloration.
  • Patients should always discuss their current state of health and medical history with their doctor before starting a course of amoxicillin.

What is amoxicillin?

Amoxicillin belongs to a group of drugs called the penicillins. They originate from a form of fungi called Penicillium fungi.

Penicillins are antibiotic drugs. They are used to treat infections caused by bacteria and to eliminate the bacteria.

Amoxicillin fights bacteria and stops them from growing by preventing them from forming cell walls. This kills the bacteria and eventually eradicates the infection.

Amoxicillin and other antibiotics are not known to be effective against viral infections, such as colds and flu.


As an antibiotic, amoxicillin is used to treat infections caused by bacteria.

Conditions that amoxicillin can treat include:

  • bronchitis
  • ear infection
  • gonorrhea
  • Lyme disease
  • pneumonia
  • skin infections
  • throat infections
  • tonsillitis
  • typhoid
  • urinary tract infections

It is not effective against the common cold or flu viruses. Using it for these purposes increases the risk of antibiotic resistance and further infection.

Other uses

Amoxicillin can be used in combination with another antibiotic called clarithromycin to treat stomach ulcers caused by H. pylori bacterial infection.

These drugs can also be combined with lansoprazole to help reduce stomach acid and symptoms of acid reflux.

Health care providers sometimes prescribe amoxicillin for heart problems, to prevent chlamydia during pregnancy, to prevent bacterial infection in newborns, or to protect the heart valve after surgical procedures.

Amoxicillin can also be used "off-label" to treat anthrax.

Amoxicillin should only be used "off-label," in other words, for purposes not usually specified, if specifically recommended by a healthcare provider.

How is amoxicillin taken?

Amoxicillin can be taken orally as a dry tablet, a chewable tablet, a capsule, a suspension, or liquid preparation, or as drops for children.

Amoxicillin is normally taken either twice a day, every 12 hours, or three times a day, every 8 hours, depending on the doctor's instruction.

It may be taken with or without food, and the liquid form can be mixed with other liquids such as baby formula, fruit juice, milk, and water.

Liquids and drops should be shaken thoroughly before use to ensure that the medication is distributed evenly.

Tablets and capsules should be taken with water, and chewable tablets should be fully chewed before swallowing.

It is important to follow the exact dosage and frequency as instructed by health care providers.

If a dose is missed, one should be taken as soon as possible unless it is nearly time for the next dose. Never take a double dose to make up for a missed one.

Even if symptoms resolve, the patient must follow the treatment course to the end.

Discontinuing treatment before the end of the prescribed course increases the risk of bacteria developing a resistance to the antibiotic. The infection could also return.

Adverse effects and interactions

If a patient is short of breath after taking amoxicillin, it may be an allergic reaction. Urgent medical attention is advised.

Like many forms of medication, amoxicillin can have unwanted side effects.

Some of these are more common, and some are more severe.

It is most important for doctors to check whether the patient is allergic to penicillin because an anaphylactic reaction can be fatal.

Signs and symptoms of an allergic reaction include:

  • chest tightness
  • difficulty breathing
  • rash or hives
  • itchiness
  • swelling of the face or throat

Anyone experiencing any of these symptoms while taking amoxicillin should seek urgent medical attention.

Between 1 and 10 percent of patients will experience an upset stomach, possibly with vomiting and diarrhea, due to Clostridium difficile (C. difficile) infection.

This is because the antibiotic changes the gut flora. Most cases are mild, but fatal colitis can occur.

Between 1 and 10 percent will develop candidiasis, a fungal or myotic infection.

Patients who are concerned about these side effects should contact their doctor.

Some people experience vaginal itching or a swollen, black tongue that feels "hairy."

Less common but more serious adverse effects include:

  • severe skin rash or hives
  • seizures
  • yellowing of the eyes or skin or dark-colored or bloody urine
  • pale skin
  • unusual bleeding or bruising
  • fatigue

These require medical attention.

Women who are pregnant or breastfeeding should not take amoxicillin. It can pass into breast milk.

This is not a full list of adverse effects. For more information and a full list of adverse effects, patients should check the patient information leaflet (PIL) that comes with the medication or speak to their healthcare provider.

Drug interactions

It is very important that a doctor is aware of what medication a patient is taking before prescribing amoxicillin.

Amoxicillin works well with some forms of medication such as clarithromycin and lansoprazole, but with other drugs, there may be unwanted interactions.

Interaction can occur with:

  • anticoagulant drugs such as warfarin
  • treatments for gout, such as probenecid and allopurinol
  • other antibacterials, such as chloramphenicol, macrolides, sulfonamides, and tetracycline
  • methotrexate, used in cancer therapy
  • some muscle relaxants
  • oral typhoid vaccine

Interactions include:

  • increasing or reducing the effectiveness of other drugs
  • increasing toxicity by reducing the body's ability to excrete the drug after use

All of these are potentially hazardous.

Amoxicillin can also affect the results of certain diagnostic tests, such as urine glucose tests. This could lead to false positive results.

Doctors and other health care providers must be fully informed of any other drugs, treatments or tests that a patient is being given before they prescribe amoxicillin.

They may need to change the dosage or take extra precautions.

Anyone who takes an overdose should call their local poison center at 1-800-222-1222.

Amoxicillin and birth-control measures

Amoxicillin may reduce the effectiveness of birth control measures, such as patches, rings, or the birth control pill.

A secondary prevention method such as condoms may be needed during the treatment course.

Anyone who is using these methods of birth control should discuss their options with their physician or health care provider.

Other precautions

Although amoxicillin can treat certain infections effectively, repeated use can reduce its effectiveness.

A 20-year study published in the BMJ in 2014 found that 1 in 10 of all antibiotic prescriptions failed to treat the infection. The number of antibiotic failures has been rising.

This would appear to indicate a growing tendency toward antibiotic resistance, where overuse of antibiotics is reducing their effectiveness.

For this reason, doctors need to be sure that the patient's condition is caused by a bacteria, and to know if a patient has previously used amoxicillin.

Alcohol does not affect the antibiotic activity of amoxicillin, but patients should avoid drinking alcohol while an active infection is present. This can support the body in effectively eradicating infection.

The use of alcohol may also mask side effects that can occur with amoxicillin, increasing the potential for complications.

Health care providers should also know if the patient has any of the following conditions:

  • allergy to penicillin or cephalosporin antibiotics
  • asthma
  • hay fever
  • hives
  • kidney disease
  • mononucleosis
  • phenylketonuria

Being clear and concise with doctors and health care providers will ensure the safe and effective use of amoxicillin.

Amoxicillin (Video Medical And Professional 2020).

Section Issues On Medicine: Medical practice