Denmark-based Lundbeck ( HLUKF ) sells tetrabenazine in the U.S. under the brand name Xenazine and reported $253 million in sales in 2013. There are no patents protecting tetrabenazine in the U.S. and orphan drug exclusivity ends next year. Zacks analyst Jason Napodano believes Auspex can fend off generic versions of tetrabenazine with SD-809's better tolerability and safety profile, reaching peak sales in Huntington's of $232 million. The more lucrative commercial opportunity for Auspex and SD-809 will come from developing the drug and receiving approval in other movement disorders, including tardive dyskinesia and Tourette's syndrome. Combined, the latter two indications could boost peak sales of SD-809 to more than $1 billion, projects Napodano.