Inhalable insulin is a powdered form of insulin, delivered with an inhaler into the lungs where it is absorbed. In general inhaled insulins have been more rapidly absorbed than subcutaneous injected insulin, with faster peak concentration in serum and more rapid metabolism. Exubera, developed by Inhale Therapeutics (later named Nektar Therapeutics), became the first inhaled insulin product to be marketed, in 2006 by Pfizer, but poor sales led Pfizer to withdraw it in 2007. Afrezza, a monomeric inhaled, ultra rapid-acting insulin developed by Mannkind, was approved by the FDA in 2014 and is the only inhaled insulin commercialized at the moment. History Insulin was discovered by Sir Frederick G Banting, Charles H Best, and JJR Macleod from the University of Toronto in 1921 as an injectable agent. German researchers first introduced the idea of inhalable insulin in 1924. Years of failure followed until scientists realized they might be able to use new technologies to turn insulin into a concentrated powder with particles sized for inhalation. In the 1980s Nektar Therapeutics developed technology to make insulin into small particles, technology then licensed to Pfizer. Alkermes developed a delivery device that they licensed to Eli Lilly and Company. Once concrete methods were developed, human tests began in the late 1990s. In January 2006, the U.S. Food and Drug Administration (FDA) approved the use of Exubera, a form of inhalable insulin developed by Pfizer. It was approved in the UK in August 2006 but reimbursed by the National Health Service only for people who had problems with needles. It was not reimbursed by any US insurer. A 2007 systematic review concluded that the inhaled hexameric insulin (Exubera) "appears to be as effective, but no better than injected short-acting insulin. The additional cost is so much more that it is unlikely to be cost-effective." In 2007, Pfizer announced that it would no longer manufacture or market Exubera. According to Chairman and CEO Jeffrey Kindler this was because Exubera "failed to gain acceptance among patients and physicians". At the time of Exubera's discontinuation, several other companies were pursuing inhaled insulin including Alkermes working with Eli Lilly and Company, MannKind Corporation, and Aradigm working with Novo Nordisk. By March 2008, except for MannKind's Afrezza product, all of these products had been discontinued because investors all decided to withdraw funding. On March 16, 2009 MannKind submitted a new drug application for their inhalable insulin. In 2011 the