Ketolide

Ketolides are a class of antibiotics that are structurally related to macrolides. They are used to treat bacterial infections, particularly those caused by Gram-positive bacteria. Ketolides are derived from erythromycin, a well-known macrolide antibiotic, and have been modified to overcome some of the limitations associated with macrolides, such as resistance and poor pharmacokinetics.

Structure and Mechanism of Action

Ketolides are characterized by their macrolactone ring, which is a large cyclic ester. This ring is similar to that found in macrolides, but ketolides have a 3-keto group instead of the cladinose sugar, which is a distinguishing feature. This modification enhances their binding to the bacterial ribosome, specifically the 50S subunit, thereby inhibiting protein synthesis.

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Telithromycin, a ketolide antibiotic

The mechanism of action of ketolides involves binding to the 23S rRNA of the 50S ribosomal subunit, which blocks the exit tunnel of the ribosome and prevents the elongation of the nascent peptide chain. This action is similar to that of macrolides, but ketolides have a higher affinity for the ribosomal target, making them effective against some macrolide-resistant strains.

Clinical Uses

Ketolides are primarily used to treat respiratory tract infections, including community-acquired pneumonia, acute bacterial sinusitis, and chronic bronchitis. They are particularly useful in treating infections caused by Streptococcus pneumoniae, including strains that are resistant to other antibiotics.

Resistance

Bacterial resistance to ketolides can occur through several mechanisms, including mutations in the ribosomal RNA, efflux pumps that expel the antibiotic from the bacterial cell, and enzymatic modification of the antibiotic. However, ketolides are generally more resistant to these mechanisms compared to macrolides due to their structural modifications.

Adverse Effects

The use of ketolides can be associated with several adverse effects. Common side effects include gastrointestinal disturbances such as nausea, vomiting, and diarrhea. More serious adverse effects can include hepatotoxicity, which has been a concern with some ketolides, leading to restrictions in their use.

Examples of Ketolides

The most well-known ketolide is telithromycin, which was the first ketolide to be approved for clinical use. Telithromycin is effective against a wide range of respiratory pathogens and is used in the treatment of community-acquired pneumonia and other respiratory infections.

Related pages

• Macrolide
• Antibiotic resistance
• Bacterial ribosome