Metaproterenol is no longer available in the United States. The manufacturer of this medication decided to stop making it in order to comply with regulations concerning chlorofluorocarbons (CFCs), chemicals that may deplete the ozone layer. The product was rarely used anymore; had it been more popular, the manufacturer probably would have chosen to reformulate it without CFCs, instead of just discontinuing it.
This article focuses on the metaproterenol inhaler. Metaproterenol also comes in tablets, syrup, and a solution that is inhaled using a machine called a nebulizer.