The macrolides (erythromycin,
azithromycin, clarithromycin, dirithromycin, troleandomycin, etc.) bind reversibly
to the 23S rRNA in the 50S subunit. There is evidence that they may inhibit elongation of the protein by preventing
the enzyme peptidyltransferase from forming peptide bonds between the amino
acids. They may also prevent
the transfer of the peptidyl tRNA from the A-site to the P-site as shown here.