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What is Azithromycin?

The human body naturally contains trillions of bacteria. In fact, it is estimated that bacterial cells outnumber human cells 10 to 1 in the human body.  These bacteria do not usually harm us, and actually perform functions that are useful to the human body. For example, there are between 500 and 1000 bacterial species present in the human gut that are extremely important for our health as they have the ability to metabolize vitamins and synthesize vitamin K. The exact types and amount of bacterial species depends on our diet and lifestyle. Our bodies naturally co-exist with this healthy ‘microflora’ and are usually harmless. However, when we come into contact with harmful bacteria or ‘pathogens’ that are not normally present in our bodies, this can lead to infection making us sick. Additionally, overgrowth of any single species of bacteria that is normally present in our body over normal microflora level can also give us unwanted symptoms. Overall, the balance of bacterial species within our body is important for the maintenance of good health. 

Infection due to bacterial growth requires the treatment of antibiotics. Antibiotics are drugs that can kill bacteria that cause infections in the human body. Before antibiotics were discovered, treatment of even simple infections was extremely challenging and often resulted in mortality. The accidental discovery of the first antibiotic, penicillin, from mold by Alexander Fleming in the 1920’s led the way to a new era in medicine. Within 15 years of its discovery, penicillins were successfully being used to treat bacterial infections. Today, as long as infections are diagnosed and treated promptly with antibiotics, bacterial infections no longer hold the same level of threat to humans as they did before the discovery of antibiotics. Since the discovery of penicillin almost 100 years ago, many other classes of antibiotics have been discovered and optimized for their ability to effectively treat infections. Formerly life-threatening infections like pneumonia or meningitis are now mostly treatable illnesses given the right antibiotic treatment regimen. Is Azithromycin a penicillin? While penicillins belong to the first generation antibiotics, later classes of antibiotics that can successfully kill more bacterial species have been discovered from nature, like Azithromycin, and based on these natural compounds, highly efficacious synthetic derivatives have been created. 

The Macrolide Antibiotics

The macrolide class of antibiotics has a characteristic lactone ring in their chemical structure. The first 15-membered lactone ring structure was synthesized by a group of scientists at Pliva laboratories in Croatia. This soon-to-be revolutionary antibiotic was called Azithromycin. Azithromycin was developed based on the structure of the first macrolide that was discovered in nature in the early 1950’s- Erythromycin. Erythromycin was isolated from the soil species, Streptomyces erythreus, and is a ‘broad-spectrum’ antibiotic, meaning that it can kill a large range of organisms. Its use became more widespread for patients that were allergic to penicillin, and it showed moderate efficacy against bacterial species like Staphylococcus aureus, Haemophilus influenzae, Mycoplasma pneumoniae, Chlamydia and Legionella species. One big drawback of Erythromycin was that it was converted into an inactive form upon contact with stomach acid. The ‘oral bioavailability’ of Erythromycin was also only decent, with only a maximum of 50% reaching the indicated tissues and body fluids. 


The chemical structure of Erythromycin gave scientists a lot of flexibility to design synthetic derivatives that could have a higher oral bioavailability and also retain their stability in stomach-acid. In the 1980’s, Pliva Laboratories was the largest pharmaceutical company in Croatia and a leading pharmaceutical company in Southeast Europe. Today, Pliva is presently a part of the TEVA group. They uniquely modified the chemical structure of Erythromycin to introduce a new group of macrolide antibiotics, called the azalides, of which Azithromycin became the first member. For their discovery, scientists at Pliva received the highest honor for their outstanding contribution to chemistry by being awarded the “Heroes of Chemistry” Award by the American Chemical Society in the early 2000s. 

What advantages does Azithromycin have over Erythromycin? 

Azithromycin also displayed broad-spectrum activity against all species that Erythromycin is effective against. But, there were a few distinct advantages between its ability to halt the growth of bacteria compared to Erythromycin. Importantly, it was four times more potent than Erythromycin against some bacterial species like Haemophilus influenzae, and at least two times more potent against other species like Campylobacter and Legionella species. Significantly, it was also found that the concentration required to inhibit the growth of species like EscherichiaSalmonellaShigella, and Yersinia was very low (less than 4 μg/ml) compared to Erythromycin (16-128 μg/ml). Toxicity studies also showed that Azithromycin was less than half as toxic as Erythromycin. Another advantage of Azithromycin was that it demonstrated rapid tissue penetration meaning that it could remain in the body tissues longer after it was taken. These features allow Azithromycin to be taken as a single dose in a daily regimen, which is a major advantage over conventional macrolides and other classes of antibiotics. In the case of Erythromycin or other antibiotics, faster elimination of the antibiotic from the body requires taking more frequent and potentially higher doses to achieve clearing of the bacteria.

Importantly, Azithromycin also proved to be highly acid-stable compared to Erythromycin, meaning that it would retain its activity when taken orally and contacted with stomach acid. What is Azithromycin used for? Evaluation of Azithromycin found it to be highly effective for treatment of upper respiratory tract infections, lower respiratory tract infections, skin infections, and sexually transmitted diseases like gonorrhea. All in all, the creation of Azithromycin was a high-impact achievement by scientists that paved the way to treat bacterial infections in a systematic and robust way. 

From Pliva to Pfizer 

When Azithromycin was first created, although Pliva was a pharmaceutical leader in Southeast Europe, marketing the new antibiotic on a global platform was not feasible for them on their own. They patented Azithromycin around the world, including in the United States. This patent record was found by pharmaceutical giant, Pfizer Inc. who immediately became interested in acquiring rights to market the drug. Pfizer, being a multinational company, had the means to do this within the U.S. and in other countries since it had offices and representatives around the world. Pfizer struck a deal with Pliva, and by the late 1980s Pfizer was marketing Azithromycin around the world, except in Central and Eastern Europe where Pliva was still selling Azithromycin under their name. In exchange for marketing Azithromycin around the world, Pfizer gave some of their royalties to Pliva. Pliva sold Azithromycin under the brand name Sumamed, while Pfizer marketed it as Zithromax. Azithromycin sold by Pfizer soon became one of the best-selling antibiotics in the U.S. 

This was much bigger than just a smart business deal for Pfizer though. The agreement between Pliva and Pfizer made Azithromycin available to patients around the world. This was, in fact, a big milestone in the way infectious diseases could be treated, especially for patients with a penicillin allergy. When the Pliva patent for Azithromycin expired in 2006, generic Azithromycin could be sold, making it more affordable and accessible to patients who are prescribed the medication for bacterial infections.  

Today, Azithromycin is prescribed for both adults and children in varying dosages according to the location of infection and bacterial species that is the cause of the infection. Most commonly, Azithromycin is prescribed for community-acquired pneumonia, sinus infections, skin infections, upper respiratory tract infections and even a sexually transmitted disease. Since it is effective for a wide-range of bacterial infections, it is no surprise that Azithromycin is one of the leading antibiotics prescribed annually in the U.S. One common misconception is that antibiotics can be used to treat viral infections like the common cold and flu, strep throat, or to treat fungal infections. All antibiotics, including Azithromycin, do not have any effect on viral or fungal infections and are specific to bacterial infections. 

How to buy and save on Azithromycin 

Where can I buy Azithromycin? If you develop symptoms of a bacterial infection and consult your doctor, you may be given anAzithromycin prescription to help you fight the infection. It is important that antibiotics are taken promptly and according to the directions given to you by your doctor. Even if your symptoms resolve before your prescribed course is over, continue to take the entire course to prevent the infection from recurring or being unable to treat a recurring infection with the same antibiotic in the future. Azithromycin can be purchased as a generic form, or as the brand Zithromax or Zpak. 

There are ways to help you save on costs of taking antibiotics like Azithromycin. Drug coupons are available from USA Rx that can substantially reduce the cost of buying Azithromycin. These drug coupons can be printed and presented to your pharmacy along with your prescription. For additional savings on more than one prescription drug, a convenient pharmacy discount card is available. Signing up is simple and can be done online in just a few minutes. Enter your name and contact details, print the card, and present it at your pharmacy when filling your prescription. This card can help you save on all FDA-approved prescription drugs, so if you are taking more than one drug, this discount card is right for you. With this discount card, you can be confident that you will be paying the lowest price for prescription drugs. 

Published March 23rd, 2020 by Chris Riley
Fact Checked by Chris Riley

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