Brief Introduction to Erythrocin

Posted on  January 6, 2021, Edited by Jason, Category  

What is erythrocin?

1. Definition

Erythrocin, is clinically mainly used for tonsillitis, scarlet fever, diphtheria and carriers, gonorrhea, listeriosis, streptococcus pneumoniae lower respiratory tract infection caused by streptococcus (the above applies to patients who are intolerant to penicillins.) It can still be used for upper respiratory tract infections caused by influenza bacillus, Staphylococcus aureus skin and soft tissue infections, syphilis, intestinal amebiasis, etc.

If you drink milk at home, BALLYA can also do an erythromycin test to let you know if there are erythromycin residues in the milk you drink in 10min.

2. Traits

This product is one kind of macrolide antibiotics, made from the culture broth of the actinomycete Streptomyces erythreus isolated from the soil on the island of Panay. It was first published by EliLilly in 1952. Several analogues such as erythromycin B and C are produced in the culture solution at the same time, and the difference in solvent solubility is used to remove them.

This product is white or light yellowish white crystalline powder, odorless, bitter, hygroscopic in the air, soluble in ethanol, chloroform, acetone and ether, and slightly soluble in water. The solubility increases after salt formation. It is relatively stable in a dry state, and the aqueous solution is relatively stable under refrigeration, and the potency gradually decreases at room temperature. It is unstable when exposed to acid, and is relatively stable when slightly alkaline, and its potency is significantly reduced below pH 4.

3. Pharmacological effects

Erythrocin is a kind of basic antibiotic produced by Streptomyces erythreus, belonging to the macrolide group. Erythromycin is a bacteriostatic agent, but it also has a bactericidal effect on highly sensitive bacteria at high concentrations.

Erythromycin mechanism of action is that it can penetrate the bacterial cell membrane to reversibly bind to the 50S subunit of the bacterial ribosome near the donor site ("P" position), blocking transfer ribonucleic acid (tRNA) from binding to the "P" position, and also blocking the displacement of the polypeptide chain from the receptor position ("A" position) to the "P" position. This process inhibits the synthesis of bacterial protein and thus has an antibacterial effect. Erythromycin is only effective against bacteria that divide actively.

Erythromycin has a broad antibacterial spectrum and is effective against most gram-positive bacteria, some gram-negative bacteria and some atypical pathogenic bacteria. Erythrocin has strong antibacterial activity against Staphylococcus (including enzyme-producing strains), various groups of streptococci, pneumococcus, Bacillus anthracis, Fusobacterium tetani, Diphtheria, Neisseria gonorrhoeae, Meningococcus, Influenza bacillus, Pertussis, Campylobacter jejuni Genus, Legionella, Listeria, and Israel Actinomycetes. It also has a good inhibitory effect on Treponema pneumoniae, Mycoplasma pneumoniae, Leptospira, Rickettsia, Chlamydia, etc.

After erythromycin lactobionate is absorbed, it is hydrolyzed to release the active ingredient erythromycin. Erythromycin can penetrate the bacterial cell membrane and reversibly bind to the bacterial ribosome.

4. Pharmacokinetics

Oral erythrocin is 200-250 mg, and the plasma concentration reaches its peak after 2 to 3 hours, which is generally less than 1 μg/ml. Except for cerebrospinal fluid and brain tissue, the drug is widely distributed in various tissues and body fluids after absorption, especially the concentration in liver, bile and spleen is higher (the concentration in bile can reach 10-40 times the concentration of blood). The concentration of the drug in kidney, lung and other tissues can be several times higher than that of the blood; there are also higher concentrations in subcutaneous tissues, sputum and bronchial secretions (the concentration in sputum is similar to the concentration in blood); in the chest and abdominal cavity, the concentration in pus can reach the effective inhibitory concentration.

Erythromycin can enter the prostate and seminal vesicles in a certain amount (about 33% of the blood concentration), but it does not easily penetrate the blood-cerebrospinal fluid barrier. When the meninges are inflamed, the concentration in the cerebrospinal fluid is only about 10% of the blood concentration. Erythromycin can enter the blood circulation of the fetus and breast milk. The fetal blood concentration is 5% to 20% of the maternal blood concentration, and the blood concentration in breast milk can reach more than 50%. After oral administration of different salts of erythromycin, the bioavailability is about 30% to 65%. The apparent volume of distribution is 0.9L/kg.

The protein binding rate is 70% to 90%. The half-life is about 1.4-2.0h, and the half-life of anuria patients can be extended to 4.8-6.0h. Free erythromycin is metabolized in the liver, mainly concentrated in the liver and excreted from the bile. Approximately 2% to 5% of the oral dose and 10% to 15% of the injection volume are filtered from the glomerulus and excreted in the urine. The concentration in urine can reach 10-100μg/ml. In addition, the stool also contains a certain amount of medicine. Peritoneal dialysis and hemodialysis cannot effectively remove erythrocin.

Erythromycin lactobionate is water-soluble, which reaches the peak blood concentration after intravenous infusion. If you infuse of 2g intravenously within 24h, the average blood concentration will be 2.3-6.8 mg/L.

What is erythrocin used for?


1. Erythrocin Uses

This product is one kind of macrolide antibiotics. Its antibacterial spectrum is similar to penicillins. It is resistant to Gram-positive bacteria, such as Staphylococcus, Streptococcus pyogenes, Streptococcus viridans, Streptococcus pneumoniae, Streptococcus faecalis, Streptococcus hemolyticus, Clostridium Bacillus, Diphtheria, Bacillus anthracis, etc. It also has a certain inhibitory effect on gram-negative bacteria, such as Neisseria gonorrhoeae, Helicobacter, Pertussis, Brucella, Legionella, Meningococcus, Haemophilus influenzae, Bacteroides, part of Shigella and Escherichia coli.

In addition, it has inhibitory effect on mycoplasma, actinomycetes, spirochetes, rickettsiae, chlamydia, nocardia, a few mycobacteria and amoeba. Staphylococcus aureus and other Staphylococcus and Streptococcus bacteria. It is characterized by strains that are resistant to penicillin and sensitive to the product. The mechanism of action is than it mainly combines with the 50S subunit of ribonucleoprotein body, inhibiting peptide acyltransferase, affecting the translocation process of ribonucleoprotein body, and hindering peptide chain growth and bacterial protein synthesis.

2. Indications

  • Acute tonsillitis, acute pharyngitis, sinusitis caused by hemolytic streptococcus, streptococcus pneumoniae, etc.
  • Scarlet fever and cellulitis caused by hemolytic streptococcus.
  • Mycoplasma pneumoniae pneumonia, Chlamydia pneumoniae pneumonia.
  • Gas gangrene, anthrax, tetanus.
  • Diphtheria (adjuvant treatment) and diphtheria carriers.
  • Chlamydia trachomatis conjunctivitis.
  • Urogenital infection caused by Chlamydia and Mycoplasma.
  • Listeriosis.
  • Legionella pneumonia (legionellosis).
  • Neisseria gonorrhoeae infection.
  • Campylobacter jejuni enteritis.
  • Oral infection caused by anaerobic bacteria.
  • Whooping cough.
  • Actinomycosis.
  • Dermatology is mainly used for non-gonococcal urethritis (cervicitis), gonorrhea, syphilis, chancroid, chlamydial lymphogranuloma (venereous lymphogranuloma), acne, and Staphylococcal skin infections, scarlet fever, etc.

How to use erythrocin?

1. Contraindications

Erythrocin can pass through the placental barrier and enter breast milk. Pregnant and lactating women and those who are allergic to macrolides should use it with caution.

2. Usage and erythromycin dosage

  • Common oral dosage: 1 to 2g per day, divided into 3 to 4 times. Legionnaires' disease: The daily dose can be increased to 2 to 4 g, divided into 4 doses. Local administration: To treat trachoma, conjunctivitis, and keratitis, apply an appropriate amount of ointment to the eyelids several times a day. Dose for renal insufficiency: patients with impaired renal function generally do not need to reduce the dosage.
  • Children: Oral administration: 30-50 mg/kg per day, 3 to 4 times. Local administration: for trachoma, conjunctivitis, keratitis, apply an appropriate amount of ointment to the eyelids several times a day.
  • Intravenous drip: Adults: General dosage: 1~2g per day, divided into 2~4 times. Legionnaires' disease: 3 to 4g per day, administered in 4 divided doses. The high dose cannot exceed 4g. Children: 20-40 mg/kg per day, divided into 2 to 4 times.

What are the side effects of erythrocin?


1. Erythromycin Side Effects 

  • Gastrointestinal symptoms such as diarrhea, nausea, vomiting, mid-upper abdominal pain, and loss of appetite may occur after medication. The incidence is related to the dose.
  • Hepatotoxicity such as fatigue, jaundice and abnormal liver function may occasionally occur after mcedication.
  • Large doses (≥4g per day) may cause ototoxicity in patients with liver or kidney disease, or in elderly patients. It is mainly manifested as hearing loss. It may be related to high blood concentration (>12 mg/L), and most of them can return to normal after stopping the drug.
  • Occasionally, allergic reactions such as drug fever, rash, and eosinophilia may occur after medication, and the incidence is about 0.5% to 1%.
  • A few patients have occasional arrhythmia, and oral or vaginal Candida infections after medication.
  • Some patients may occasionally experience venous irritation or phlebitis after intravenous administration.

2. Precautions

  • Erythromycin is a bacteriostatic drug. The administration should be carried out at a certain interval to maintain the concentration of the drug in the body and facilitate its effect.
  • Erythromycin tablets should be swallowed perfectly. If the powder is taken, it will be destroyed by gastric acid and the effect will be reduced. Young children can take acid-stable esterified erythrocin.
  • Intravenous drip is easy to cause phlebitis, so the drip speed should be slow.
  • Erythromycin destroys and lowers the effect in acidic infusions, so it generally should not be compatible with low-pH glucose infusions. In 500ml of 5%~10% glucose infusion, add vitamin C injection (1g sodium ascorbate) or 0.5ml of 5% sodium bicarbonate injection to raise the pH above 5, and add erythromycin lactobionate, will help the stability.

3. Drug Interactions

  • Erythromycin is used together with antiepileptic drugs such as carbamazepine and valproic acid, which can inhibit the metabolism of carbamazepine and valproic acid, causing the latter to increase its blood concentration and occur toxic reactions. And carbamazepine can reduce the efficacy of erythromycin through liver microsomal oxidase.
  • The combination of erythromycin and cyclosporine can promote the absorption of cyclosporine and interfere with its metabolism. The clinical manifestations are abdominal pain, hypertension and liver dysfunction.
  • The use of erythromycin and xanthines (except dihydroxyprophylline) can reduce the hepatic clearance of aminophylline, leading to increased serum aminophylline concentration and/or increased toxicity. This phenomenon is more likely to occur after 6 days, and the reduction of aminophylline clearance is proportional to the peak erythromycin serum.
  • The combination of erythromycin and digoxin can clear the intestinal flora that can inactivate digoxin, thereby causing digoxin intestinal hepatic circulation, increasing the blood concentration of digoxin and causing toxic reactions.


Erythrocin has antibacterial effects on many bacteria and can replace penicillin in some cases. Therefore, erythromycin has a wide range of uses and good effects. But we should also pay attention to the side effects and drug interactions of erythromycin.


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