antibioticsbooks

Macrolides and
Ketolides
11
Agents: clarithromycin, azithromycin,
erythromycin, telithromycin (a ketolide)
Macrolides are among the antibiotics used most
frequently in the outpatient setting because of their
broad coverage of respiratory pathogens. Though
their coverage is broad, it is not particularly deep,
because there is increasing resistance to these
agents (especially in Streptococcus pneumoniae).
To combat this resistance, the ketolide derivatives
(including telithromycin) have been introduced
with better coverage of resistant S. pneumoniae.
Unfortunately, telithromycin appears to have a significant
risk of hepatotoxicity. Although erythromycin
is the class patriarch, because of its adverse
effects, drug interactions, and frequent dosing, it
has little use except as a GI stimulant.
Mechanism of Action
Macrolides and ketolides bind to the 50S subunit
of bacterial ribosomes, preventing the ribosomes
from shuffling along and adding a new amino acid
to the elongating protein chain.