Macrolide antibiotics are antibiotics composed of 12-16 carbon skeleton of macrolide part and 1-3 aminosugars, 14, 15, and 16 metacyclic rings represent the number of carbons in the macrolide skeleton, 14, 15, and 16 metacyclic derivatives are mainly the drug structure is different, of course, there is also a certain relationship with the antibacterial properties of the drug.

Classification:

1, 14 metacyclic: e.g., erythromycin, roxithromycin, clarithromycin, dirithromycin, etc.

2, $15 ring: azithromycin.

3. $16 ring: e.g., guillamycin, madicillin, spiramycin, crossamycin, rotamycin.

Characterization of macrolide antibiotics:

1. Acts by hindering the synthesis of bacterial proteins.

2. It has powerful antibacterial effect on G+ bacteria, and has antibacterial effect on certain G-cocci, mycoplasma, chlamydia and legionnaires' disease. Effective against penicillin-resistant Staphylococcus aureus.

3. Antibacterial activity is enhanced in alkaline environment, often alkalizing urine to treat urinary tract infections.

4., There is a dense cordial cross-resistance present among macrolides.

5, not easy to pass the blood-brain barrier.

6. Mainly excreted through bile, with high concentration in bile.

7. Mainly cleared by hepatic metabolism, use with caution in hepatic insufficiency. Erythromycin esterified has a certain degree of hepatotoxicity, should be used in small quantities for a short period of time.

Key differences between erythromycin and azithromycin

1, the antimicrobial spectrum is not the same:Azithromycin has a broader antimicrobial spectrum than erythromycin and has a wider range of applications.

2, the antibacterial activity is not the same:Azithromycin has more antibacterial activity against Mycoplasma pneumoniae and Chlamydia than erythromycin.

3. The half-life is different:Azithromycin has a long half-life, so it only needs to be taken once a day, while erythromycin has a short half-life and needs to be taken 2-4 times a day.

4. The incidence of adverse reactions is not the same:Azithromycin has a low incidence of gastrointestinal reactions and hepatic impairment, while erythromycin has a higher incidence of gastrointestinal reactions and hepatic impairment compared to azithromycin, and there is a correlation with dose.

5. Drug interactions are not the same:Azithromycin and theophylline have no clinically significant interactions; whereas erythromycin can cause abnormally high concentrations of theophylline and increased toxicity and should be used with caution.

Macrolide antibiotics are a class of weakly basic antibiotics produced by streptomycin, and their structure is characterized by the molecule containing a lactone structure of the 14- or 15- or 16-membered macrocyclic ring, the 14-membered ring is mainly erythromycin, clarithromycin, and roxithromycin; the 15-membered ring is mainly azithromycin; and the 16-membered ring is mainly acetylspiramycin, madithromycin, melphalanomycin, guillotine, and sympathomycin. As shown below:

I. $14 lactone ring, representative drug: erythromycin

Erythromycin is an oral antibiotic discovered in 1952 from the metabolites of Streptococcus erythropolis. Because of its strong gastrointestinal reaction, its oral dosage form was prepared as enteric-coated tablets; its weakly alkaline character, which is unstable in acid, is easily destroyed by gastric acid and easily decomposed and inactivated, erythromycin was made into various esters and salts precursors, such as erythromycin lactobionate on the market. Its structure is shown below, there are 14 vertices in the polygonal closed ring in the red line area, each vertex represents a carbon atom, i.e., a 14-membered ring.

II. $15 lactone ring, representative drug: azithromycin

Azithromycin is a second-generation macrolide antibacterial drug, and its structure is characterized by the introduction of a methyl-substituted N atom on the basis of the original 14-membered lactone ring, so that the original 14-sided shape becomes 15-sided, i.e., 15-membered ring. Its oral absorption is fast, so it is prepared into oral preparations; compared with erythromycin, the incidence of adverse reactions is lower, gastrointestinal reactions and occasional liver function abnormalities and peripheral leukocyte decline, etc. It can be prepared into children's preparations, such as azithromycin dry suspension. The structural formula is shown in Fig:

III. $16 lactone ring, representative drug: madecassicin

Madecassicin is a macrolide antibiotic produced by the Sichuan Institute of Antimicrobial Research in China in 1974 from the isolation of Sangmiga streptomycin Sichuan var. mycarofacieus sichuanesis n. var. from the forest soil of Nanchuan Pharmaceutical Institute's specimen garden. Its ring is a 16-sided, i.e., 16-membered ring consisting of 15 carbon atoms and 1 oxygen atom as vertices, as shown in the figure:

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How do I share this with you in layman's terms?

You can think of macrolide antibiotics as having a ring of 6 carbons in the main part, some have 14, some 15, some 16, but the main indications are all similar.

For this ring, the general public does not need to know the difference between a 14-ring and a 16-ring macrolide antibiotic.

But you need to know: what are the classifications of antibiotics!

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