Eicosanoid, including prostaglandin (PG), thromboxane (TX), leukotriene (LT), and lipoxin (LX), is critical signaling molecule. Prostanoid, a subset of eicosanoids, comprises PG and TX. Prostanoids are named based on the number of carbon-carbon double bonds in their molecules. Most biologically active PGs and TXs belong to the series 2 molecules with two carbon-carbon double bonds.