Metered-dose inhaler stringent set of criteria, they must: In the early days of MDIs the most commonly used propellants were the chlorofluorocarbons CFC-11, CFC-12 and CFC-114. In 2008 the Food and Drug Administration announced that inhalers using chlorofluorocarbons as a propellant, such as Primatene Mist, could no longer be manufactured or sold as of 2012. This followed from the U.S. decision to agree to the 1987 Montreal Protocol on Substances that Deplete the Ozone Layer. Phospholipids are important natural surfactant lipids used in enhancing penetration and bioavailability. Phospholipids act by reducing the high surface tension forces at the air-water interface within the
Subnetwork Access Protocol necessary to determine which protocol is to be invoked to process a service data unit delivered by the lower layer. The most common reference to SAP, including a Source Service Access Point (SSAP) and a Destination Service Access Point (DSAP) refers to the boundary between the Data Link Layer and the Network Layer. It is common to think of SAP only in terms of its use at Layer 2, specifically in its Logical Link Control (LLC) sub-layer as defined in the IEEE 802.2 standards. Link Service Access Point (LSAP) includes both Destination Service Access Point (DSAP) and Source Service Access