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.
The first patents for Sustiva expired in August 2012 and November 2013. However, generic versions are not yet available. This strongly suggests that other patents or exclusivity rights are still providing significant protection against generic competition. The next patent set to expire will do so in September 2014.