Colistin (polymyxin E) is an important constituent of the polymyxin class of cationic polypeptide antibiotics. Intrarenal oxidative stress can contribute to colistin-induced nephrotoxicity. Nicotinamide adenine dinucleotide 3-phosphate oxidases (Noxs) are important sources of reactive oxygen species. Among the various types of Noxs, Nox4 is predominantly expressed in the kidney.