Retapamulin is a bacterial protein synthesis inhibitor belonging to a class of compounds called pleuromutilins. These compounds inhibit the initiation of protein synthesis by binding to a specific site on the 50S subunit of bacterial ribosome (domain V of 23S rRNA). This binding site involves ribosomal protein L3 and is in the region of the ribosomal P site and peptidyl transferase center. By virtue of binding to this site, pleuromutilins inhibit peptidyl transfer, block P-site interactions, and prevent the normal formation of active 50S ribosomal subunits.
Retapamulin is a semisynthetic pleuromutilin antibiotic. This drug is usually bacteriostatic in action, but may become bactericidal at highed concentrations (when MBC is 1000 times higher than MIC). Retapamulin acts by selectively inhibiting the initiation of protein synthesis in bacteria at the level of bacterial 50S ribosome.
In vitro studies with human liver microsomes demonstrated that retapamulin is extensively metabolized to numerous metabolites, of which the predominant routes of metabolism were mono-oxygenation and N-demethylation. The major enzyme responsible for metabolism of retapamulin in human liver microsomes was cytochrome P450 3A4 (CYP3A4).