Erythromycin: An Overview

Mechanism of Action

The mechanism of action of erythromycin, a macrolide antibiotic, involves inhibiting bacterial protein synthesis. This process occurs through binding to the 50S ribosomal subunit of bacteria, specifically at the ribosomal exit tunnel. By binding to this site, erythromycin prevents the movement of the newly synthesized peptide chain from the ribosome, inhibiting the elongation of the protein.

Erythromycin's binding to the ribosome interferes with the translocation of peptidyl-tRNA from the A-site to the P-site on the ribosome. This disruption prevents the addition of new amino acids to the growing peptide chain, ultimately leading to the inhibition of protein synthesis. Moreover, erythromycin also has been found to stimulate the dissociation of the peptidyl-tRNA from the ribosome, further impairing protein synthesis. This dual mechanism of action contributes to the bacteriostatic effect of erythromycin, as it halts bacterial growth and replication.

Figure 1. Erythromycin inhibits the translocation of the polypeptide chain from A site to P site.
(Source: Ahmed, F. W. et al., 2011)

The exact mechanisms underlying the anti-inflammatory and immunomodulatory effects of erythromycin are unknown. Erythromycin has been reported to reduce oxidative production of cytokines by neutrophils (IL-1, IL-6, IL-8, and TNF). Additionally, IL-10 production and platelet count are increased.

Adverse Effects of Erythromycin

Erythromycin, while generally well-tolerated, can cause various adverse effects.

• Gastrointestinal Side Effects: The most commonly reported side effects of erythromycin involve the gastrointestinal (GI) system. These include nausea, vomiting, abdominal cramps, and diarrhea. The severity of these side effects is dose-dependent. These effects are linked to erythromycin's ability to stimulate GI motility as a motilin receptor agonist.
• Allergic Reactions: In rare cases, erythromycin can trigger allergic reactions. Symptoms may include fever, eosinophilia (increased eosinophil count in the blood), and skin eruptions. Cholestatic hepatitis, characterized by an inflammatory reaction in the liver, has also been reported. These allergic reactions may be due to hypersensitivity to erythromycin.
• Thrombophlebitis: Intravenous infusion of erythromycin can occasionally lead to thrombophlebitis, which is inflammation of the veins along with the formation of blood clots. This can cause pain, redness, and swelling in the affected area.
• Cardiac Effects: Erythromycin has the potential to affect cardiac electrical activity. It can prolong the QT interval, leading to a heart rhythm disorder called torsades de pointes. This condition is more common in patients with pre-existing cardiac disease.
• Myasthenia Gravis: Erythromycin can worsen the symptoms of myasthenia gravis. Additionally, in rare cases, it can induce myasthenic-like symptoms in individuals without pre-existing myasthenia gravis.

Detection of Residual Erythromycin

The extensive use of erythromycin drugs in production leads to its residues in livestock and poultry tissues, honey, milk, fish and shrimp, and other products, posing a risk to public health. Currently, there are two main categories of methods for detecting erythromycin residues.

One is a method that allows for simultaneous separation and analysis. These methods employ highly efficient separation techniques and high detection sensitivity, enabling qualitative and quantitative analysis of residual erythromycin. Examples of such methods include high-performance liquid chromatography (HPLC), gas chromatography (GC), thin-layer chromatography (TLC), gas chromatography-mass spectrometry (GC-MS), and liquid chromatography-mass spectrometry (LC-MS).

The other type is a qualitative and semi-quantitative biological method for erythromycin, which has the characteristics of high selectivity and low detection limit. This method mainly includes enzyme-linked immunoassay (ELISA), microbial method, and radioimmunoassay.

Efficient and accurate detection of erythromycin residues is crucial to ensure food safety and protect public health. These methods, whether based on separation and analysis or biological approaches, play a significant role in monitoring and regulating erythromycin residues in various food products.