Ann: MYX announces patent lawsuit against Sun Pharmaceutical, page-5

This is a pretty standard practice by Sun Pharmaceuticals. When submitting an ANDA to the FDA (for a generic equivalent of the reference product Imvexxy) the applicant is required to challenge any existing patents (Paragraph IV subset for an ANDA filing). It is then standard practice for the sponsor of the innovator product to defend the patents (within 30 days). By doing this irrespective of the validity of patents the generic applicant can get 6 months of exclusivity over any other generic versions that are the subject of an ANDA filing. It is common that the sponsor of the innovator product will launch their own generic version before the competitor (patent protection can be assigned to the generic) can bring theirs onto the market. This most commonly happens when a patent is nearing its expiry date.