Maduramicin ammonium is prepared from maduramicin by taking advantage of the acidic carboxylic acid which ionises and readily forms the salt in ammonium hydroxide solutions. The ammonium salt is the preferred formulation in animals to prevent coccidiosis and to promote growth. Maduramicin is also active against Treponema and Cryptosporidium. Maduramicin is an ionophore, forming complexes with monovalent cations, with a higher affinity for K+ than Na+.