Application Narasin is a growth-promoting ionophoric antibacterial agent for Enterococci, specifically Enterococcus faecium and Enterococcus faecalis1,2. It inhibits coccidial infection in poultry and mammals and is used in studies involving sodium calcium ion exchange. Biochem/physiol Actions Narasin administration in swine results in improved nitrogen digestibility, which decreases fecal nitrogen and increases the relative concentrations of propionic acid in the large intestine. Polyether ionophores, such as Narasin, have a hydrophilic interior and a hydrophobic exterior. The lipophilic ionophore attaches to the lipid rich cell membranes of Gram-positive bacteria. Ionophores bind Na+, K+, and H+ and facilitate their transfer across the bacterial cell membrane, resulting in an increase in H+ concentration on the inside of the Gram-positive cell. Therefore, the H+ ATPase pump is activated to transport out excess H+. The cell is depleted of its energy resources and reduces fermentative functions and cell division 3.