Maduramicin is a polyether ionophore antibiotic that has been found in Nocardia. It selectively binds to potassium, rubidium, sodium, lithium, and cesium ions over divalent cations. Maduramicin is active against Gram-positive bacteria (MICs = 0.9-125 µg/ml) but not Gram-negative bacteria (MICs = >1,000 µg/ml) or fungi (MICs = 250->1,000 µg/ml). It reduces the viability of asexual and gametocyte P. falciparum parasites (EC50s = 1.3 and 14.8 nM, respectively) and reduces P. berghei transmission in a mouse model of malaria when administered at doses of 4 and 8 mg/kg. Maduramicin (5-10 ppm in the diet) reduces the severity of lesions and completely protects chicks against mortality in a model of coccidiosis induced by E. tenella.1 Formulations containing maduramicin have been used in the treatment of coccidiosis in chickens.