Ketolides are antibiotics belonging to the

macrolide The Macrolides are a class of natural products that consist of a large macrocyclic lactone ring to which one or more deoxy sugars, usually cladinose and desosamine, may be attached. The lactone rings are usually 14-, 15-, or 16-membered. Ma ...

group. Ketolides are derived from erythromycin by substituting the cladinose sugar with a keto-group and attaching a cyclic carbamate group in the

lactone Lactones are cyclic carboxylic esters, containing a 1-oxacycloalkan-2-one structure (), or analogues having unsaturation or heteroatoms replacing one or more carbon atoms of the ring. Lactones are formed by intramolecular esterification of the co ...

ring. These modifications give ketolides much broader spectrum than other macrolides. Moreover, ketolides are effective against macrolide-resistant bacteria, due to their ability to bind at two sites at the bacterial ribosome as well as having a structural modification that makes them poor substrates for efflux-pump mediated resistance.Bertram G. Katzung, Susan B. Masters, Anthony J. Trevor ''Basic & Clinical Pharmacology, 11e'' McGraw-Hill 2009 via "accessmedicine.com" Ketolides block protein synthesis by binding to ribosomal subunits and may also inhibit the formation of newly forming ribosomes. According to a recent study comparing the action of the classic macrolides erythromycin and

azithromycin Azithromycin, sold under the brand names Zithromax (in oral form) and Azasite (as an eye drop), is an antibiotic medication used for the treatment of a number of bacterial infections. This includes middle ear infections, strep throat, pneumo ...

with ketolides, which are used to treat serious infections, the more powerful drugs (ketolides) were the more "leaky" in blocking the production of proteins. The researchers were surprised to discover that ketolides, which are known to be better antibiotics, allow for many more proteins to be made compared to the older, less efficient macrolides. As a result, it is now believed that allowing cells to make some proteins could be much more damaging for a microbe than not letting it make any proteins at all. The findings may point the way to better and more potent antibiotics. The only ketolide on the market at this moment is

telithromycin Telithromycin is the first ketolide antibiotic to enter clinical use and is sold under the brand name of Ketek. It is used to treat community acquired pneumonia of mild to moderate severity. After significant safety concerns, the US Food and Drug ...

, which is sold under the brand name of Ketek. Other ketolides in development include

cethromycin Cethromycin, trade name Restanza (initially known as ABT-773) is a ketolide antibiotic undergoing research for the treatment of community acquired pneumonia (CAP) and for the prevention of post-exposure inhalational anthrax, and was given an "or ...

and solithromycin.

Medical uses

Ketolides are used to treat community-acquired

bacterial pneumonia Bacterial pneumonia is a type of pneumonia caused by bacterial infection. Types Gram-positive '' Streptococcus pneumoniae'' () is the most common bacterial cause of pneumonia in all age groups except newborn infants. ''Streptococcus pneumonia ...

. Other

respiratory tract infections Respiratory tract infections (RTIs) are infectious diseases involving the respiratory tract. An infection of this type usually is further classified as an upper respiratory tract infection (URI or URTI) or a lower respiratory tract infection (LRI ...

were removed as indications when it was recognized that use of

can result in

hepatitis Hepatitis is inflammation of the liver tissue. Some people or animals with hepatitis have no symptoms, whereas others develop yellow discoloration of the skin and whites of the eyes ( jaundice), poor appetite, vomiting, tiredness, abdominal ...

and liver failure.

References

{{Protein synthesis inhibitor antibiotics