Immediate release market is small, sonata has been a commercial dud for three different companies, elan and king and I can't remember who elan got it from. The problem is for $100M a year in peak sales, you'd need to spend half that amount in marketing just to get it. If mr were approved, ir marketing costs zero, so it's accretive. No MR and I'd question if it's even worth launching.
Sepracor has different doses of lunesta, higher strength and a lower strength for more of an ir profile. I haven't seen any data on what the sales split is.
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