Please also see Exenatide LAR, the once-weekly formulation of exenatide.

GLP-1 is an incretin hormone secreted in the small intestine and colon in response to food intake. It enhances insulin secretion when glucose levels are high, suppresses inappropriate glucagons secretion (glucagon has the opposite effect of insulin), slows gastric emptying (slowing entry of ingested nutrients into the bloodstream, hence limiting post-prandial glucose), and via actions on the brain is thought to promote satiety.

Amylin’s exenatide is a synthetic version of a peptide derived from Gila monster lizard venom. Amylin had acquired exclusive patent rights to this compound and another "exendin" in October 1996 from their discoverer. While GLP-1 has a half-life less than 2 minutes, exenatide has a terminal half-life of 2.4 hours.

In May 2008, Amylin and Lilly entered into an addendum to their co-promotion agreement, or the Addendum, pursuant to which Lilly added a third party sales force to co-promote BYETTA in the United States.

In April 2009, Amylin and Eli Lilly agreed to an amendment of the collaboration agreement between the parties made in September 2002. The Amendment requires Lilly to give Amylin one year notice of any termination without cause of the Collaboration Agreement. Prior to amending the agreement, Lilly was required to provide six months notice of any termination without cause.

The parties also clarified allocation and reimbursement procedures of certain shared expenses under the terms of the Collaboration Agreement. They also agreed to adopt a set of guidelines to govern the working relationship of an integrated medical, development and commercial team for exenatide comprised of Amylin employees and Lilly employees to be located in San Diego.

In June 2009, Amylin and Lilly mutually agreed to terminate the Addendum entered in May 2008 effective as of June 30, 2009. The underlying co-promotion agreement remains intact and Amylin and Lilly continue to co-promote BYETTA.