Some previous drug shortages have been due to scarcity of underlying raw materials, particularly of the active pharmaceutical ingredient (API) for a specific drug. Generic drug manufacturers frequently have only one supplier of API, so if this supplier is unable to meet demand, the drug manufacturer must find another source and this can be a challenge. Changes in manufacturing components may also present challenges. Appropriate alternatives for the raw materials or components must be found that works within the manufacturing process. Changes in raw materials or other manufacturing components must be validated by the drug manufacturer. Once validated, the changes must be approved by the FDA through a supplement to the abbreviated new drug application. Once FDA has reviewed and approved the supplement, which FDA can expedite if the product is in shortage and medically necessary, the manufacturer can begin production using the new raw material or component. API supply failures have been the cause of some high-impact drug shortages. For example, the heparin shortage in 2008 resulted from the import of contaminated raw materials from China. However, although scarcity of raw materials cannot be ignored as a root cause, it does not appear to be an important contributor to the current shortages of sterile injectable drugs. In 2010, unavailable API was cited as a factor in 5 percent and component problems in 2 percent of shortages.