Chapter 198 Macrolides
INTRODUCTION
Macrolides represent a large group of similar compounds that are all products of Streptomyces spp. Biochemically they are characterized by a macrocyclic lactone ring attached to one or more sugar moieties. Macrolides with the greatest clinical efficacy generally are derived from erythromycin. It should be noted that azithromycin is not technically a macrolide, but rather an azalide. It generally is grouped with the macrolides because it shares most of their properties.
MECHANISM OF ACTION
All macrolides work by reversibly binding the 50s ribosome. This results in suppression of ribonucleic acid–dependent protein synthesis. Macrolides are bacteriostatic at clinical concentrations. They are particularly effective against gram-positive organisms and Mycoplasma spp. In addition, they have fair efficacy against anaerobic organisms. Many macrolides are actively concentrated in macrophages. This can result in very high drug concentrations at the site of infection.1
PHARMACOLOGY
In general, macrolides are characterized by low serum concentrations and large volumes of distribution. They are concentrated in tissues including the lung, heart, and macrophages. Newer macrolides such as azithromycin have high oral bioavailability (40% to 60%) and long half-lives. The main route of excretion is through bile and the intestinal tract.2
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