Monensin is the polyether ionophore antibiotic, which is produced by fermentation of Streptomyces cinnamonensis. It is active against certain gram-positive microorganisms primarily against coccidia, such as Eimeria acervulina, E. mivat, E. brunetti, E. maxima, E. necatrix, E. tenella in broiler chickens.
Monensin acts on the trophozoite in the first cycle of schizogony. The mechanism by which monensin acts is based on its ability to form complexes with sodium and potassium ions and to prevent penetration across the cell membrane of coccidia. Monensin prevents sodium transport while potassium is accumulated in the cell of the parasite thereby inhibiting mitochondrial functions of the parasite, oxidation and hydrolysis of adenosine triphosphate.
In ruminants with developed forestomachs monensin increases the rate of weight gain and enhances feed efficiency.