Colistin, also known as polymyxin E, is an antibiotic medication used as a last-resort treatment for multidrug-resistant Gram-negative infections including pneumonia. These may involve bacteria such as Pseudomonas aeruginosa, Klebsiella pneumoniae, or Acinetobacter. It comes in two forms: colistimethate sodium can be injected into a vein, injected into a muscle, or inhaled, and colistin sulfate is mainly applied to the skin or taken by mouth. Colistimethate sodium is a prodrug; it is produced by the reaction of colistin with formaldehyde and sodium bisulfite, which leads to the addition of a sulfomethyl group to the primary amines of colistin. Colistimethate sodium is less toxic than colistin when administered parenterally. In aqueous solutions it undergoes hydrolysis to form a complex mixture of partially sulfomethylated derivatives, as well as  colistin. Resistance to colistin began to appear as of 2015.Common side effects of the injectable form include kidney problems and neurological problems. Other serious side effects may include anaphylaxis, muscle weakness, and Clostridium difficile-associated diarrhea. The inhaled form may result in constriction of the bronchioles. It is unclear if use during pregnancy is safe for the fetus. Colistin is in the polymyxin class of medications. It works by breaking down the cytoplasmic membrane, which generally results in bacterial cell death.Colistin was discovered in 1947 and colistimethate sodium was approved for medical use in the United States in 1970. It is on the World Health Organizations List of Essential Medicines. The World Health Organization classifies colistin as critically important for human medicine. It is available as a generic medication.
Hyperoxia occurs when cells, tissues and organs are exposed to an excess supply of oxygen (O2) or  higher than normal partial pressure of oxygen.In medicine, it refers to excess oxygen in the lungs or other body tissues, which can be caused by breathing air or oxygen at pressures greater than normal atmospheric pressure. This kind of hyperoxia can lead to oxygen toxicity, caused from the harmful effects of breathing molecular oxygen at elevated partial pressures. Hyperoxia is the opposite of hypoxia; hyperoxia refers to a state in which oxygen supply is excessive, and hypoxia refers to a state in which oxygen supply is insufficient. In the environment, it refers to excess oxygen in a body of water or other habitat. Signs and symptoms
Associated with hyperoxia is an increased level of reactive oxygen species (ROS), which are chemically reactive molecules containing oxygen. These oxygen containing molecules can damage lipids, proteins, and nucleic acids, and react with surrounding biological tissues. The human body has naturally occurring antioxidants to combat reactive molecules, but the protective antioxidant defenses can become depleted by abundant reactive oxygen species, resulting in oxidation of the tissues and organs.The symptoms produced from breathing high concentrations of oxygen for extended periods have been studied in a variety of animals, such as frogs, turtles, pigeons, mice, rats, guinea pigs, cats, dogs and monkeys. The majority of these studies reported the occurrence of irritation, congestion and edema of the lungs, and even death following prolonged exposures.