There are various forms of statins, some of which include atorvastatin, fluvastatin, lovastatin, pitavastatin, pravastatin, rosuvastatin, and simvastatin. Combination preparations of a statin and another agent, such as ezetimibe/simvastatin, are also available. The class is on the World Health Organization's List of Essential Medicines with simvastatin being the listed medicine. In 2005, sales were estimated at in the United States. The best-selling statin is atorvastatin, also known as Lipitor, which in 2003 became the best-selling pharmaceutical in history. The manufacturer Pfizer reported sales of in 2008. Due to patent expirations, several statins became available in 2016 as less expensive generics.