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What is the Difference Between Amoxicillin and Penicillin?

Amoxicillin and penicillin are both antibiotics, but amoxicillin is a broader spectrum variant, meaning it can fight a wider range of bacteria. Penicillin is often used for more specific infections. While both stem from the same family, their effectiveness and dosage requirements differ. Wondering which is right for your ailment? Let's examine their uses and side effects further.
Tricia Christensen
Tricia Christensen
Tricia Christensen
Tricia Christensen

The antibiotics amoxicillin and penicillin are close relatives. Amoxicillin is a derivative of penicillin, and it was first isolated in 1972, while penicillin was discovered in the 1920s and first saw significant use toward the end of World War II. Scientists developed drugs like amoxicillin because penicillin was not always useful in treating all infections, and the two drugs work in similar ways by inhibiting cell wall growth of bacteria. Each drug has similar action against a variety of bacteria, but they do have differences that are worth noting. Some of these differences include the way they are made, their effectiveness against certain bacteria, and their side effect profile.

One way that amoxicillin differs from penicillin is how it is made. Amoxicillin is semi-synthetic, which means it is a natural substance that is transformed by application of certain chemicals. Penicillin is a synthetic drug, meaning it is created out of several dynamic laboratory processes.

Amoxicillin an an oral medication is often as effective as injected penicillin.
Amoxicillin an an oral medication is often as effective as injected penicillin.

The way that amoxicillin and penicillin differ in terms of effectiveness is often contested. It is known that amoxicillin has a higher penetration rate and a longer half-life. It also treats more types of bacteria than does penicillin. Amoxicillin is called a moderate spectrum drug, while penicillin is called a narrow spectrum drug.

Oral preparations of amoxicillin are often as effective as injected forms of penicillin for a variety of conditions. For instance, some studies found that oral amoxicillin was just as effective as injected penicillin to treat children with bacterial pneumonia. Amoxicillin may work more effectively over a shorter time period than penicillin. The drug can also be combined with clavulanate to treat bacteria that produce beta-lactamase.

Amoxicillin can lead to anaphylaxis in those with a penicillin allergy.
Amoxicillin can lead to anaphylaxis in those with a penicillin allergy.

There are many side effects that amoxicillin and penicillin share. Both can upset the stomach, and are especially known for causing diarrhea. Amoxicillin is thought to cause more stomach upset problems than penicillin, but some researchers assert the opposite is true. Also, the rate at which people feel side effects varies by the individual, and it’s possible for patients to have fewer side effects than would be clinically predicted.

Vomiting and diarrhea are the most common side effects of amoxicillin.
Vomiting and diarrhea are the most common side effects of amoxicillin.

Amoxicillin and penicillin are both associated with a high rate of allergic reaction. It’s not uncommon for people to have an anaphylactic allergic reaction to one of these drugs, and people allergic to one medicine are urged to avoid the other. Anaphylaxis can be detected by symptoms such as difficulty breathing, rash or hives, swelling of the mouth, face, and tongue, and feelings of faintness, sense of doom, and nausea. If these symptoms arise when a patient is taking either medicine, he or she needs emergency medical care.

Like other antibiotics, both amoxicillin and penicillin can cause unpleasant and even serious side effects.
Like other antibiotics, both amoxicillin and penicillin can cause unpleasant and even serious side effects.

Ultimately, these substances are more alike than different. Amoxicillin has greater application and can treat more types of bacteria, but both drugs share approximately equal efficacy in a variety of infections. Amoxicillin tends to be prescribed more often than penicillin.

Tricia Christensen
Tricia Christensen

Tricia has a Literature degree from Sonoma State University and has been a frequent TheHealthBoard contributor for many years. She is especially passionate about reading and writing, although her other interests include medicine, art, film, history, politics, ethics, and religion. Tricia lives in Northern California and is currently working on her first novel.

Learn more...
Tricia Christensen
Tricia Christensen

Tricia has a Literature degree from Sonoma State University and has been a frequent TheHealthBoard contributor for many years. She is especially passionate about reading and writing, although her other interests include medicine, art, film, history, politics, ethics, and religion. Tricia lives in Northern California and is currently working on her first novel.

Learn more...

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    • Amoxicillin an an oral medication is often as effective as injected penicillin.
      By: Oleksii Nykonchuk
      Amoxicillin an an oral medication is often as effective as injected penicillin.
    • Amoxicillin can lead to anaphylaxis in those with a penicillin allergy.
      By: jinga80
      Amoxicillin can lead to anaphylaxis in those with a penicillin allergy.
    • Vomiting and diarrhea are the most common side effects of amoxicillin.
      By: elisabetta figus
      Vomiting and diarrhea are the most common side effects of amoxicillin.
    • Like other antibiotics, both amoxicillin and penicillin can cause unpleasant and even serious side effects.
      By: Alliance
      Like other antibiotics, both amoxicillin and penicillin can cause unpleasant and even serious side effects.
    • Liquid amoxicillin may be administered to children in lieu of pills.
      By: ognianmed
      Liquid amoxicillin may be administered to children in lieu of pills.
    • Penicillin allergies can be serious, and CPR may be necessary if the person experiencing anaphylaxis is not breathing.
      By: Photographee.eu
      Penicillin allergies can be serious, and CPR may be necessary if the person experiencing anaphylaxis is not breathing.
    • Warning signs of an allergic reaction may include a swollen tongue.
      By: Deyan Georgiev
      Warning signs of an allergic reaction may include a swollen tongue.
    • A syringe is recommended for giving exact dosages of liquid amoxicillin to young children and babies.
      By: Rachakrit
      A syringe is recommended for giving exact dosages of liquid amoxicillin to young children and babies.