Erythromycin Vs. Azithromycin

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 [¹]. 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 [²]. Both drugs act by binding to the 23S ribosomal RNA molecule in the 50S subunit in susceptible bacteria to stop protein synthesis.

About Erythromycin and Azithromycin

What is Erythromycin?

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. [³] 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. [⁴]

Respiratory infections (throat and chest-related infections).
Skin infections.
Gastrointestinal infections (digestive tract and intestinal infections).
Genital infections (infections affecting sexually active body parts).

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. [⁵] This inhibition process results in the control of various bacteria-induced infections in the body.

What is Azithromycin?

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. [⁶] When administered orally, Azithromycin is concentrated within macrophages and polymorphonucleocytes. It is also concentrated in phagocytes and fibroblasts. [⁷]

What Conditions Is Azithromycin Approved to Treat?

Azithromycin is approved to treat the following conditions. [⁸]

Chronic obstructive pulmonary diseases (diseases that cause airflow blockage and breathing-related issues).
Acute bacterial sinusitis (nasal cavity and sinusitis infections).
Community-acquired pneumonia (a type of lung infection).
Tonsilitis (tonsil-related infections).
Cervicitis and urethritis (urethra and cervix-related infections).
Genital ulcer disease in males (genital infections).

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. [⁹] 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. [¹⁰]

Effectiveness

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 2016 comparative study 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 2007 study 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 2004 comparative study 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.

Dosage Information

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. [¹¹]

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. [¹²]

Side Effects

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. [¹³]

Nausea
Vomiting
Abdominal Discomfort
Diarrhea
Anorexia
Abnormal Liver Function Test Results

Are There Any Potential Serious Side Effects of Erythromycin?

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

Allergic Reactions (Urticaria or Anaphylaxis)
Skin Reactions (Mild Eruptions or Erythema Multiforme)
Stevens-Johnson Syndrome
Toxic Epidermal Necrolysis
Pancreatitis and Convulsions (rare cases)

What are the Most Common Side Effects of Azithromycin?

The common side effects in some cases of Azithromycin use may include the following. [¹⁴]

Abdominal Discomfort
Nausea
Vomiting
Diarrhea
Rashes

Are There Any Potential Serious Side Effects of Azithromycin?

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

Allergic Reactions (Arthralgia, Edema, Urticaria, and Angioedema)
Ventricular Tachycardia (A Cardiovascular Problem)
Hypotension (A Cardiovascular Problem)
Acute Renal Failure (Kidney Problem)
Hepatitis

Contraindications and Interactions

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. [¹⁵]

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. [¹⁶]

Contraindications and Important Interactions for Erythromycin and Azithromycin

Contraindications

Erythromycin

Do not take the drug if you have know hypersensitivity to similar macrolides
Do not take the drug if you are taking terfenadine, astemizole, pimozide, or cisapride

Azithromycin

Do not take the drug if you have know hypersensitivity to similar macrolides
Do not take the drug if you have a history of cholestatic jaundice associated with a similar drug

Drug/Medication Interactions

Erythromycin

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)

Azithromycin

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

The drug may potentiate the effects of warfarin when taken concomitantly

Food/Beverage/Supplement Interactions

Erythromycin

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

Azithromycin

Alcohol may increase the adverse effects of the drug

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

Cost Comparison

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 here.

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 top 225th drug in 2020 with an estimated 2,091,152 prescriptions in the country in the same year. On the other hand, Azithromycin has been ranked the top 68th drug in the same year, 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 dispensed products in 2020. On the contrary, Azithromycin 500mg tablets had a 12.9%, and 250mg tablets had an 80.7% of dispensed products in the same year.

Conclusion

Takeaway

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.