Master Macrolides with Picmonic for Medicine

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Macrolides are a group of antibiotics whose activity stems from the presence of a macrolide lactone ring. Commonly used macrolides include erythromycin, azithromycin, and clarithromycin. As a class, these drugs bind to the 23S rRNA of the 50S prokaryotic ribosomal subunit and inhibit protein synthesis via blocking of translocation. These antibiotics are considered to be bacteriostatic and are commonly used against gram positive cocci, atypical pneumonias, and infections caused by Chlamydia. Bacteria can become resistant to macrolides via alteration of the 23S rRNA binding site, usually by post-transcriptional methylation. Macrolides are potent inhibitors of the cytochrome P450 system, especially CYP3A4. Therefore, macrolides can cause elevations of other drugs metabolized by the P450 system. One particular combination that should be avoided due to this interaction is macrolides with statins, used for lowering cholesterol, which can lead to debilitating myopathy. Macrolides, especially erythromycin and clarithromycin also have an effect on QT prolongation, which can lead to torsade de pointes if untreated. These drugs exhibit enterohepatic recycling meaning the drug is absorbed in the gut and sent to the liver where it is excreted back into the duodenum in bile. This form of recycling can lead to a buildup of the product and cause nausea and GI distress like diarrhea. There is also a strong association of macrolides and hepatotoxicity. The pathogenesis of hepatotoxicity with macrolide exposure involves both a direct cytotoxic affect as well an immunoallergic reaction. Hepatoxicity caused by an immunoallergic reaction is typically accompanied by peripheral eosinophilia and skin rash.

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Bacteriostatic antibiotics limit the growth of bacteria by interfering with bacterial protein production, DNA replication, or other aspects of metabolism while not necessarily directly harming the organism. Upon removal of the bacteriostatic agent, the bacteria can regrow as opposed to bactericidal agents that directly kill bacteria.

A macrolide antibiotic with similar spectrum as the other macrolide drugs. Erythromycin is especially associated with GI disturbances because erythromycin is a motilin agonist. Due to this, erythromycin is sometimes used in treating gastroparesis. It is also associated with prolonged QT intervals that can lead to Torsades.

Azithromycin, commonly called Zithromax or Zmax, is a macrolide antibiotic derived from erythromycin. This drug is commonly used to prevent bacterial infections, especially middle ear infections, strep throat, pneumonia, and sinusitis. It is also effective against sexually transmitted infections including Chlamydia. Azithromycin has been associated with cardiovascular effects; specifically, prolongation of the QT interval. Prolongation of the QT interval can lead to torsades de pointes (TdP), an abnormal heart rhythm, which can be fatal.

Clarithromycin is a macrolide antibiotic typically used to treat pharyngitis, tonsillitis, maxillary sinusitis, pneumonia, and acute bacterial exacerbation of chronic bronchitis. Unlike erythromycin, clarithromycin is acid stable and can be taken orally without being protected from gastric acids. Of all the drugs in its class, clarithromycin has the best bioavailability, which makes it more amenable to oral administration.

Macrolides inhibit protein synthesis by interfering with the elongation of the polypeptide chain of bacterial proteins and the translocation of the ribosomal subunit. These antibiotics bind to the 23S ribosomal RNA in the 50S subunit, which catalyzes the formation of the peptide bond.

Gram positive cocci are gram positive organisms that absorb crystal violet on gram stain due to thick peptidoglycan layer with a spherical shape. Gram positive cocci include Staphyloccus and Streptococcus species. Macrolides are effective against gram positive cocci.

Atypical pneumonias are typically characterized by a protracted course, lack of sputum production, and extra-pulmonary symptoms as compared to typical pneumonia. Common causes of atypical pneumonias include Mycoplasma pneumoniae, Chlamydia, and Legionella. Macrolide antibiotics are commonly used in the treatment of atypical pneumonias.

Chlamydia trachomatis is an obligate intracellular human pathogen that has three human serovars that cause diseases including trachomas, urethritis, and lymphogranuloma venereum. Macrolides can also be used to treat infections caused by Chlamydia pneumoniae and Chlamydia psittaci.

Bacteria can become resistant to macrolides via alteration of the 23S rRNA binding site, usually by post-transcriptional methylation.

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