The downgrade to 'sell' and 'market underperform' is due to significant challenges with Xphozah's reimbursement and modest growth from Ibsrela. The inclusion of Xphozah in a bundled system and loss of Medicare Part D coverage limits revenue potential. Additionally, increased SG&A expenses and looming debt obligations raise concerns about Ardelyx's ability to achieve consistent profitability and fund necessary R&D investments, which are critical for future growth.