Is Azithromycin a Penicillin?

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Penicillin was originally used to describe the drug benzylpenicillin, or Penicillin G. Now, it is used to describe a group of antibiotics that all contain a chemical beta-lactam ring structure with many natural and synthetic derivatives of the original penicillin available. One of the most commonly prescribed penicillin-type antibiotics is Amoxicillin (also known as the brand Moxatag, Amoxil or Augmentin when combined with another beta-lactamase inhibitor clavunalate potassium). Other common penicillin-type antibiotics are ampicillin or piperacillin.

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Antibiotics are drugs that can treat bacterial infections. Our bodies contain healthy bacteria that live in a specific location, like on our skin and in our colon.

When this bacteria moves to another part of the body, like in a urinary tract infection, or if we come into contact with bacteria that is not normally present in our bodies, like in the case of food poisoning cause, this results in a bacterial infection that causes unwanted symptoms and must be treated with antibiotics before we can start feeling better.  

For many people, the first thought that arises on being prescribed an antibiotic is whether it is penicillin, which was originally used to describe the drug benzylpenicillin, or Penicillin G.

Now, it is used to describe a group of antibiotics that all contain a chemical beta-lactam ring structure with many natural and synthetic derivatives of the original penicillin available.

One of the most commonly prescribed penicillin-type antibiotics is Amoxicillin, also known as the brand Moxatag, Amoxil or Augmentin when combined with another beta-lactamase inhibitor clavunalate potassium.

Other common penicillin-type antibiotics are ampicillin or piperacillin.

Many people want to know if Azithromycin, a common prescription for treating infections, is a penicillin. Let’s explore.

How does Penicillin work? 

Penicillin can prevent bacteria from multiplying by interfering with their cell wall synthesis.

The cell wall is necessary for the bacterial cell to remain intact and protect them from their surrounding, so when penicillins interfere with cell wall formation in bacteria, water can flow into the cells and results in their death. 

Penicillins are the first-line antibiotics prescribed for various infections like upper respiratory tract or sinus infections.

Their efficacy has been expanded to treat infections caused by additional organisms like Clostridium, Neisseria Listeria. 

But, many individuals are allergic to penicillin and cannot take this group of antibiotics to treat bacterial infections.

Some estimates say that almost 10% of the population is allergic to penicillin. For these individuals, alternative antibiotic classes must be prescribed that can target and kill the source of the infection.

The Macrolide Antibiotics 

Since the discovery of penicillin, several classes of antibiotics like cephalosporins and quinolone antibiotics were discovered and optimized for treatment of bacterial infections.

Of these, the macrolide class of antibiotics is especially significant. The Macrolide antibiotics were first discovered in the 1950s from the soil bacteria, Streptomyces erythreus that produced Erythromycin.

Later in the 1970s and 1980s, derivatives of Erythromycin were synthesized and named Clarithromycin and Azithromycin.

Unlike the penicillins that have a beta-lactam ring structure, the macrolides are characterized by a large-lactone ring in their chemical structure. Erythromycin is a 14-membered lactone ring. Azithromycin is synthetically modified to have a 15-member lactone ring.

How do macrolides work? 

Macrolides work by preventing bacteria from synthesizing the proteins that they need to survive and thereby resulting in halted growth or death of the bacteria if a higher concentration of the macrolide is taken.

In the United States, there are currently five macrolide antibiotics that are on the market. These include:

  • Azithromycin
  • Clarithromycin
  • Erythromycin
  • Fidaxomicin
  • Telithromycin 

Of these, Azithromycin is the most commonly prescribed macrolide.

What is Azithromycin?

Today, it is the most commonly prescribed antibiotic for bacterial infections in the United States and is the first choice antibiotic for individuals that are allergic to penicillins.

Azithromycin is known by the brand names Zithromax, ZMax or Zpak. 

Penicillin vs. Azithromycin for Bacterial Infections 

What is Azithromycin used for?

Azithromycin is commonly used to treat infections of the middle ear (otitis media), tonsillitis, sinusitis, skin infections, laryngitis, pneumonia, mycobacterial infections, and sexually transmitted diseases like gonorrhea and chlamydia.

Azithromycin is very effective against infections caused by Streptococcus pneumoniae, Mycobacterium pneumoniae, Haemophilus influenzae, and Staphylococcus aureus to name a few. 

Penicillin is used to treat infections of the middle ear, tonsils, throat, urinary tract, skin, and pneumonia. It is effective against the bacterial species E. coli, Pneumococcus, Streptococcus, Haemophilus influenzae, and some strains of Staphylococcus aureus

Penicillins and Azithromycin also have different side effects associated with their use. 

Side effects associated with penicillin include:

  • Diarrhea
  • Abdominal pain
  • Rash
  • Heartburn
  • Nausea
  • Itching 

More serious side effects like a seizure or low platelet count have also been reported to occur. Penicillins can also induce a serious allergic reaction in some individuals.

Extreme caution should be taken in taking penicillins if you have experienced an allergic reaction to any penicillin in the past.

Some penicillin-related antibiotics like the cephalosporins can also induce an allergic reaction in individuals that are allergic to penicillin. 

The major side effects of Azithromycin can be:

  • Diarrhea 
  • Nausea
  • Abdominal pain 
  • Vomiting
  • Tongue discoloration 
  • Ringing in the ears (tinnitus)

Sometimes more serious side effects like angioedema or an abnormal heartbeat can have been reported to occur.

These more serious side effects should be noted immediately and checked with your doctor. 

An advantage of Azithromycin is that it is not usually associated with the same type of allergic reactions as the penicillin-antibiotics. However, when taking a new drug for the first time, an allergic reaction is always possible.

A severe allergic reaction to Azithromycin (anaphylaxis) can occur, so if you experience any serious unwanted symptoms after taking Azithromycin, contact your doctor immediately. 

When taking any antibiotic, either Penicillin or Azithromycin, the normal growth of healthy bacteria in the colon can also be affected.

This is because the antibiotic can also prevent growth of bacteria that are important to maintaining the health of our colon along with the targeting the bacteria that causes an infection.

A decrease in the amount of healthy bacteria in our colon can result in overgrowth of bacteria that causes inflammation in the colon, causing diarrhea and severe abdominal pain. If this happens, contact your doctor immediately.

Potential Bacterial Resistance of Penicillins vs. Azithromycin 

Long-term use of an antibiotic can sometimes result in the ability of the bacteria that causes the infection to become resistant to the antibiotic.

This can also occur when an antibiotic course is not taken in completion. Either of these events means that the infection can no longer be treated with the antibiotic that the bacteria has become resistant to.

Usually, bacteria that are resistant to one class of antibiotics can be treated with another class to clear an infection, since all antibiotic classes have different ways that they defeat the bacteria.

For example, Azithromycin is used to treat Traveler’s Diarrhea in areas where the bacteria are predicted to be resistant to other classes of antibiotics, but not to the macrolide class (to which Azithromycin belongs to).

Every year, more cases of bacterial infections that cannot be treated by penicillins are reported.  This means that the ability of bacteria to become resistant to penicillins is currently a health concern.

For this reason, macrolide antibiotics, like Azithromycin, are often prescribed to treat common bacterial infections that may face complications of resistance from the penicillins. 

References and Sources:

Wikipedia – Azithromycin

medically reviewed and fact checked
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