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Amoxicillin vs. Penicillin

Tuesday 6 October 2020
5 minute(s) read

Table of Contents

I. The Role of Antibiotics

II. Uses for Penicillin

a. Side Effects of Penicillin

III. Uses for Amoxicillin

a. Side Effects of Amoxicillin

IV. So, What’s the Difference?

The Role of Antibiotics

The invention of antibiotics has changed modern medicine and the treatment of several common ailments. Antibiotics are powerful medications that fight bacterial infections and prevent deadly complications. When harmful microbes enter the body, the immune system jumps into action. The immune system creates white blood cells to attack and kill harmful bacteria. In most cases, the immune system can fight off the infection on its own. Infection can occur for several reasons, so it is important to keep an eye on your body changes. Signs of infection can include:

  • Fever
  • Chills and sweats
  • Increased urination
  • Stiff neck
  • Vomiting
  • New onset of pain
  • Redness, soreness, or swelling in areas of surgical wounds or ports
  • Unusual vaginal discharge or irritation [1]

Sometimes, the harmful bacteria outnumber the white blood cells, and a dangerous infection may occur, and you may be prescribed antibiotics like amoxicillin, Levaquin (levofloxacin), and Pen VK (penicillin V). These medications help kill bad bacteria and allow the immune system to work more efficiently. Amoxicillin is a type of penicillin. Both of these antibiotics are some of the most common on the market today.


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Penicillin and amoxicillin antibiotics work to treat different types of ailments, but it is essential not to overuse antibiotics because you may develop resistance, rendering antibiotics useless. Read on to learn more about the similarities and differences between two of the most common antibiotics, amoxicillin, and penicillin. [2]

a petri dish with penicillin microbes

Uses for Penicillin

Alexander Fleming first discovered penicillin in 1928. He found that a mold called Penicillium inhibited the growth of bacteria. After a decade of tests and trials, penicillin was hailed as a miracle drug during the Second World War because it prevented the death of thousands of men. With the invention of penicillin, bacterial infections were no longer a death sentence. This modern marvel of medicine is still used frequently, but penicillin has transformed over the years. Various derivatives of penicillin remain active against bacterium such as:

  • Listeria (foodborne bacterial illness)
  • Clostridium (tetanus and botulism)
  • E.coli (spread through contaminated food or water)
  • Certain strains of staphylococci
  • Salmonella (spread through the intestinal tracts of birds)
  • Shigella (spread through contaminated water or food or contaminated feces)

In many cases, penicillin antibiotics like Pen VK (penicillin V) can treat many common middle ear, sinus, stomach, and intestinal infections. Uses include:

  • Pneumonia
  • Blood infections
  • Meningitis
  • Endocarditis
  • Uncomplicated gonorrhea
  • Other serious infections [3]

a. Side Effects of Penicillin

Penicillin has seen many forms since its inception almost 100 years ago. Today, drugs like Penicillin V can come in the form of an oral tablet or solution. Antibiotics cannot kill viruses like strains of the seasonal flu or cold. Antibiotics must be prescribed for the right reasons; otherwise, antibiotic resistance may occur. Penicillin drugs typically have few side effects, but you may experience:

  • Nausea
  • Vomiting
  • Upset stomach
  • Diarrhea
  • Black hairy tongue

You must tell your doctor if you are allergic to any antibiotic before beginning a round of antibiotics. If you are allergic, you may experience skin reactions like a rash with blisters, flu-like symptoms, or swelling of the throat, tongue, or mouth. You may also experience diarrhea and fever if you are not reacting properly to the medication. [4]

a woman with a fever

Uses for Amoxicillin 

Amoxicillin is a type of penicillin. Both of these antibiotics are some of the most common on the market today. Amoxicillin was discovered at Beecham Research Laboratories in England in 1972. These researchers were able to narrow down specific antimicrobials of penicillins to treat a wider range of infections. Amoxicillin and its predecessor ampicillin had a broader spectrum of activity than the original penicillin. [5]

This drug works by preventing bacterial microbes from forming cell walls. Using this medication leads to the death of the bacteria and clears up the infection. Like other antibiotics, amoxicillin does not fight viral infections. Amoxicillin is commonly used for:

  • Bronchitis
  • Ear infections
  • Gonorrhea
  • Lyme disease
  • Skin infections
  • Throat infections
  • Tonsillitis
  • Typhoid
  • Urinary tract infections 

Amoxicillin can also be used in combination with other drugs like lansoprazole to treat more severe conditions like stomach ulcers and acid reflux symptoms. Amoxicillin is also used for some “off-label” purposes. This means that the drug has benefits for purposes not specifically prescribed. Off-label uses are only recommended by experienced healthcare providers.

There are also several forms of amoxicillin, including chewable tablets, capsules, suspension, and drops. It is usually taken twice a day or every 12 hours, but it depends on your doctor's advice. It is typically recommended to take these drugs with food and water to prevent unpleasant side effects. [6]

a. Side effects of Amoxicillin

It is important to discuss any previous allergies to penicillin if you are being prescribed amoxicillin. If you are allergic to penicillin, you will likely have adverse reactions to its variants as well. You may be allergic if you experience chest tightness, difficulty breathing, rash, hives, and swelling of the face or throat. Around one in 10 people will experience an upset stomach when taking this antibiotic. [6] More serious side effects may include:

  • Fatigue
  • Unusual bleeding or bruising
  • Pale skin
  • Yellowing of the eye or skin
  • Dark-colored or bloody urine
  • Seizures
  • Severe skin rash
  • Hives [6] 

a bunch of prescription pills

So, what’s the difference?

Both of these medications are effective in treating bacterial infections. Because penicillin has been used for so long, it is used less often because many bacteria strains have become resistant to its bacteria-killing effects. It can still help with common infections, but you may have to seek alternative antibiotic methods if you are antibiotic-resistant.

Amoxicillin is more commonly used today because it can treat a wider range of infections than its predecessor penicillin. This is due to decades of medical innovation and testing. So, the main difference between the two is that amoxicillin is more efficient in killing a wider range of bacteria. Many doctors are worried about antibiotic resistance, so they may only prescribe these antibiotics if your infection is severe. Talk to your doctor about the right treatment for you. [7]

The content in this article is intended for informational purposes only. This website does not provide medical advice. In all circumstances, you should always seek the advice of your physician and/or other qualified health professionals(s) for drug, medical condition, or treatment advice. The content provided on this website is not a substitute for professional medical advice, diagnosis, or treatment.