Sinapultide is a synthetic peptide used to mimic human lung surfactant protein B, the most important surfactant protein for a proper functioning of the respiratory system. Protein B lowers surface tension at the air-liquid interface of the alveolar surfaces during respiration and stabilizes the alveoli against collapse at resting transpulmonary pressures. A deficiency of pulmonary surfactant in premature infants results in respiratory distress syndrome. Sinapultide compensates for the deficiency of surfactant and restores surface activity to the lungs of these infants. Sinapultide was originally developed in the Scripps Research Institute and then licensed to Windtree Therapeutics (formerly Discovery Laboratories, Inc.). Sinapultide is the active ingredient of Lucinactant, a liquid medication to treat infant respiratory distress syndrome. Lucinactant was approved by the FDA in 2012 and sold under the trademark Surfaxin, but in 2015 it was discontinued by Discovery Laboratories, Inc in favor of Aerosurf, another drug containing Sinapultide.