Nigericin sodium is a salt of the atypical polyether antibiotic, nigericin. Since nigericin is an ionophore, its very high affinity for monovalent cations such as Na+ and K+ means that formation of a salt is a facile possess occurring during purification under any but highly acidic conditions. Typically, the salts of polyether ionophores like the free acid, are readily extracted into organic solvents. The sodium ion is stabilised within a polar pocket of the structure, effectively making the salt and free acid different chemical moieties with the potential for differing pharmacology, a fact not readily appreciated in the literature.