The lawsuits are the results of Abbreviated New Drug Applications (ANDA) filed by Eon and Impax respectively with the FDA concerning their intent to market generic omeprazole products in the US. The antisecretory drug omeprazole is marketed in the US by AstraZeneca, L.P. under the brand name Prilosec® and is marketed internationally by AstraZeneca as Losec®.

The basis of AstraZeneca's complaints are that the actions by Eon and Impax both infringe upon several patents relating to Prilosec®, which provide protection to the year 2014. Those patents include coverage for formulations and for methods for using Prilosec®. The substance patent, which expires in 2001, has not been challenged by either Eon or Impax.

AstraZeneca intends to fully enforce its patent rights and is steadfast in its belief that all of the patents are valid.