Narasin (4-methylsalinomycin) is a polyether antibiotic isolated from Streptomyces aureofaciens in 1978. Although narasin is a close analogue of salinomycin, the metabolites are produced by different species and are not co-metabolites. Narasin is an ionophore with broad spectrum activity against Gram positive bacteria including anaerobes and mycoplasma, and also possesses antiviral and limited antifungal activity. Narasin is used in the animal health industry as an in-feed antibiotic and growth promotant.