<p>Hepatic first-pass metabolism contributes significantly to erythromycin metabolism after an oral dose.<sup class="text-reference-group"><a class="reference-popover-link" data-content="Sun H, Frassetto LA, Huang Y, Benet LZ: Hepatic clearance, but not gut availability, of erythromycin is altered in patients with end-stage renal disease. Clin Pharmacol Ther. 2010 Apr;87(4):465-72. doi: 10.1038/clpt.2009.247. Epub 2010 Jan 20. (PubMed ID 20090676)" href="#reference-A174457">11</a></sup> Erythromycin is partially metabolized by CYP3A4 enzyme to N-desmethylerythromycin.<sup class="text-reference-group"><a class="reference-popover-link" data-content="FDA Approved Drug Products: Ery-Ped (erythromycin ethylsuccinate) granules for oral suspension" href="#reference-L7261">21</a>,<a class="reference-popover-link" data-content="Fohner AE, Sparreboom A, Altman RB, Klein TE: PharmGKB summary: Macrolide antibiotic pathway, pharmacokinetics/pharmacodynamics. Pharmacogenet Genomics. 2017 Apr;27(4):164-167. doi: 10.1097/FPC.0000000000000270. (PubMed ID 28146011)" href="#reference-A174175">8</a></sup> Erythromycin is also hydrolyzed to <em>anhydro</em> forms (anhydroerythromycin [AHE] and other metabolites), and this process is promoted by acidic conditions.<sup class="text-reference-group"><a class="reference-popover-link" data-content="Krasniqi S, Matzneller P, Kinzig M, Sorgel F, Huttner S, Lackner E, Muller M, Zeitlinger M: Blood, tissue, and intracellular concentrations of erythromycin and its metabolite anhydroerythromycin during and after therapy. Antimicrob Agents Chemother. 2012 Feb;56(2):1059-64. doi: 10.1128/AAC.05490-11. Epub 2011 Nov 14. (PubMed ID 22083477)" href="#reference-A174448">5</a></sup> AHE is inactive against microbes but inhibits hepatic drug oxidation and is therefore considered to be an important contributor to erythromycin drug-drug interactions.<sup class="text-reference-group"><a class="reference-popover-link" data-content="Krasniqi S, Matzneller P, Kinzig M, Sorgel F, Huttner S, Lackner E, Muller M, Zeitlinger M: Blood, tissue, and intracellular concentrations of erythromycin and its metabolite anhydroerythromycin during and after therapy. Antimicrob Agents Chemother. 2012 Feb;56(2):1059-64. doi: 10.1128/AAC.05490-11. Epub 2011 Nov 14. (PubMed ID 22083477)" href="#reference-A174448">5</a></sup></p><p class="d-none d-sm-block"><strong>Hover over products below to view reaction partners</strong></p>