In Agile, you are supposed to ship product on a regular cadence. All features are added to a product backlog, divided into small projects that fit within a sprint, and then prioritized. The backlog is just a way to keep track of all of the ideas people have, requests from customers, major bugs and other things.
The first patent for Pristiq is set to expire in February 2022. This is the earliest predictable date that a generic version of the drug could become available. However, other circumstances could come up to extend or shorten the exclusivity period.
There are maintenance fees to be paid during the life of a utility patent, and if they are not paid on time the patent will expire earlier than the maximum 20-year-from-filing term. After the patent expires, the invention is available to all. Design Patents are valid for a period of 14 years from the date of issue.