When diagnosed with bacteria-induced infections, doctors prescribe macrolide antibiotics to patients for bacterial resistance and infection treatment. Erythromycin and Azithromycin are two such antibiotics that are highly effective against certain infections. Erythromycin is a bacteriostatic antibiotic drug widely used to treat gram-positive and gram-negative bacterial infections, including respiratory, skin, gastrointestinal, and genital infections [

]. Azithromycin is a broad-spectrum macrolide (antibiotic) drug from the azalide class of macrolides with a high degree of tissue penetration. This drug is effective against respiratory, enteric, and genitourinary infections [

]. Both drugs act by binding to the 23S ribosomal RNA molecule in the 50S subunit in susceptible bacteria to stop protein synthesis. 

Erythromycin is a bacteriostatic antibiotic manufactured by a strain of Saccharopolyspora erythraea (formerly known as Streptomyces erythraeus). Discovered in 1952, this macrolide stops bacterial growth in the infected body part with the inhibition and translation of protein synthesis. [

] When administered orally, Erythromycin is readily absorbed. It accumulates in leucocytes and inflammatory liquid. 

What Conditions Is Erythromycin Approved to Treat?

Erythromycin is approved to treat various bacterial infections, including the following. [

How Does Erythromycin Work for Bacterial Infections?

When susceptible bacteria enter the body, they require specialized protein synthesis to replicate. Ribosomal proteins enable this process (of protein synthesis). Erythromycin comes into action by inhibiting protein synthesis and binding to the 23S ribosomal RNA molecule present in the 50S ribosomal subunit (in bacterial organisms). The drug stops the synthesis process by hindering the translocation part of protein synthesis and (also) by stopping the assembly of the 50S subunit of ribosomes. [

] This inhibition process results in the control of various bacteria-induced infections in the body. 

Azithromycin is a broad-spectrum macrolide belonging to the azalide subclass of macrolides. Discovered in 1988 (initially approved by the FDA in 1991), this antibiotic drug stops bacterial growth by hindering protein translation and synthesis in the infected body part. [

] When administered orally, Azithromycin is concentrated within macrophages and polymorphonucleocytes. It is also concentrated in phagocytes and fibroblasts. [

What Conditions Is Azithromycin Approved to Treat?

Azithromycin is approved to treat the following conditions. [

How Does Azithromycin Work for Bacterial Infections?

In terms of mechanism of action, Azithromycin acts similarly to Erythromycin. When absorbed, Azithromycin binds to the 23S rRNA of the 50S ribosomal unit (bacterial). The drug comes into action to stop bacterial protein synthesis by hindering the transpeptidation part of the protein synthesis. [

] It also inhibits the assembly of the 50S ribosomal subunit. This activity results in controlling various bacteria-induced infections. What makes it different from Erythromycin is the absence of drug-drug interactions as observed with Erythromycin. [

How Effective Are Erythromycin and Azithromycin for Treating Bacterial Infections?

Erythromycin and Azithromycin are highly effective against bacterial infections. They share a similar structure and vary (primarily) based on how they handle drug-drug interactions. A 

 of treating acute respiratory tract infections in children highlighted that Azithromycin once daily (3-5 days) was as effective as Erythromycin thrice daily (7 days). 

Antibiotic drugs may react differently when treating infections among pregnant women. A 

 of single-dose Azithromycin versus Erythromycin for treating Chlamydia trachomatis infection during pregnancy highlighted that both drugs were equally effective in treatment. However, Azithromycin was found to be safer (with fewer gastrointestinal adverse events) than Erythromycin. 

Bordetella pertussis is a common infection in areas with poor air quality which leads to excessive coughs. Being a bacterial infection, pertussis is treated with macrolides, such as Erythromycin and Azithromycin. A 

 analyzed the effects of both drugs in treating infection among groups of children. The study found that both antibiotic drugs were equally effective in treating pertussis. However, those who received Erythromycin faced more gastrointestinal adverse effects than the ones with Azithromycin. Azithromycin was declared safer for treating the infection as compared to Erythromycin.  

How is Erythromycin Administered for Bacterial Infections?

Erythromycin is generally suitable for oral, topical, intravenous, and ophthalmic uses. Doctors examine the patient’s condition to prescribe the best route of drug administration. [

How is Azithromycin Administered for Bacterial Infections?

Azithromycin is generally administered for oral and intravenous routes. Doctors diagnose infections in patients and prescribe the best route of drug administration. [

The following pointers cover the common and serious side effects of Erythromycin and Azithromycin. Please note that these side effects may vary based on the patient’s health history and the nature of the infection. Your doctor may advise you thoroughly on the possibility of adverse events after diagnosis. 

What are the Most Common Side Effects of Erythromycin?

You may notice the following (frequent) side effects when taking Erythromycin. [

Are There Any Potential Serious Side Effects of Erythromycin?

* If you experience any of these serious side effects, seek medical help immediately.

What are the Most Common Side Effects of Azithromycin?

The common side effects in some cases of Azithromycin use may include the following. [

Are There Any Potential Serious Side Effects of Azithromycin?

Warnings and General Precautions for Erythromycin and Azithromycin

Erythromycin is excreted by the patient’s liver to come into action. If the patient has an impaired hepatic function, the drug should be used with precaution (after discussing it with the doctor). Moreover, Erythromycin may increase weakness in patients with myasthenia gravis. [

Azithromycin may lead to cases of Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS) in some patients. When used in the absence of a bacterial infection, the drug may increase the risk of developing drug-resistant bacteria. [

Contraindications and Important Interactions for Erythromycin and Azithromycin

Concurrent use of ergotamine and Erythromycin may lead to acute ergot toxicity

The drug may increase the pharmacologic effect of triazolam and alprazolam 

The drug may increase the systemic exposure of sildenafil 

The drug maysignificantly alter the metabolism of antihistamines, terfenadine, and astemizole (nonsedating forms)

Concurrent use of nelfinavir and Azithromycin may result in increased Azithromycin serum concentrations

The drug may potentiate the effects of warfarin when taken concomitantly

When combined with alcohol, the drug may take longer to absorb and (therefore) delay its effects (to occur)

Food may decrease the levels of the drug in your body and should be taken on an empty stomach for easier absorption

Grapefruit consumption may increase the drug levels in the body

Alcohol may increase the adverse effects of the drug

Grapefruits may interact with the drug (but such reports are uncommon)

How Much Do Erythromycin and Azithromycin Cost?

Please note that the costs of Erythromycin and Azithromycin may vary based on different pharmaceutical brands. You may consult your doctor before deciding on a particular brand. 

The costs of Erythromycin tablets are mentioned below. 

100 tablets of 250mg may cost between $579.94-$791.34 ($5.80-$7.91 per tablet), making it $11.6-$15.82 per day (prescribed dosage is 2x /12 hours). 

100 tablets of 500mg may cost (on average) $1,114.87 ($11.15 per tablet), making it $11.15 per day (prescribed dosage is 1x /12 hours). 

You can thoroughly check the cost details of Erythromycin tablets 

The costs of Azithromycin tablets are mentioned below. 

100 tablets of 250mg may cost (on average) $219.65 ($2.20 per tablet), making it $4.40 per day (prescribed dosage is 2x /12 hours). 

100 tablets of 500mg may cost (on average) $429.80 ($4.30 per tablet), making it $4.30 per day (prescribed dosage is 1x /12 hours). 

You can go through the details of the price for various concentrations of Azithromycin here. 

Popularity of Erythromycin and Azithromycin

Erythromycin and Azithromycin are among the most popular antibiotic drugs for bacterial infections in the U.S. If we review the statistical data, Erythromycin was ranked the 

 with an estimated 2,091,152 prescriptions in the country in the same year. On the other hand, Azithromycin has been ranked the 

, with an estimated 10,155,807 prescriptions. 

If we narrow down to dispensed dosage forms, Erythromycin 500 mg tablets had a 17.5%, and 250mg tablets had a 12.3% of 

. On the contrary, Azithromycin 500mg tablets had a 12.9%, and 250mg tablets had an 80.7% of 

Erythromycin and Azithromycin are highly effective antibiotic drugs for a series of bacterial infections. Both drugs have been widely used in the U.S. to treat conditions such as respiratory problems, skin infections, gastrointestinal infections, and other bacteria-induced diseases. Erythromycin is more likely to develop adverse effects in patients as compared to Azithromycin. Both drugs should be used with precautions to avoid adverse drug interactions and the risk of drug-resistant bacteria in the body. 

Being highly popular, both drugs are available under various pharmaceutical brand labels. Moreover, the costs of each may vary based on the brand you choose. It is worth remembering that the choice and cost of a brand may not speak about its effectiveness. You may always consult your doctor to initiate a prescribed therapy.

Erythromycin Vs. Azithromycin

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