Exton, PA, July 29, 2026 (GLOBE NEWSWIRE) -- Access, not efficacy, stands between Ardelyx's Xphozah® (tenapanor) and a materially larger share of the dialysis hyperphosphatemia market, according to new findings from Spherix Global Insights' RealTime Dynamix™: Dialysis (US), a quarterly service designed to track prescriber perceptions, competitive dynamics, and the evolving market for phosphate-lowering therapies. Nephrologists report they would nearly triple their use of Xphozah if reimbursement and coverage barriers were removed. Yet access is only part of the challenge: physicians estimate that roughly one-third of treated hyperphosphatemia patients receive combination therapy, while Spherix patient chart data show the actual figure is closer to one in seven. Together, the findings point to a market constrained both by payer friction and by physicians’ overestimation of how aggressively uncontrolled phosphorus is already being treated.
Physicians Still Default to Diet Before Escalating Therapy
Nephrologists report that phosphorus remains the single most difficult dialysis parameter to manage, evidenced by the large share of patients who never consistently reach target. Yet despite an expanding menu of phosphate-lowering therapies, physicians often stop short of treatment escalation. Four in ten nephrologists report that their first response to persistent phosphorus elevation is renewed dietary counseling, while fewer than one in ten add Xphozah as combination therapy. Instead of switching therapies, nearly half now report increasing use of combination phosphate-lowering therapy overall—up nearly 20 percentage points from a year earlier—as they layer agents to reach target.
Even so, many patients who remain well above target continue on binder monotherapy or receive no phosphate-lowering therapy at all, underscoring a persistent gap between available treatment options and real-world therapeutic escalation.
The Most Influential Audience Isn't Always the Prescriber
A parallel Spherix study of 100 renal dietitians (RealTime Dynamix™: Dialysis Renal Dietitians (US), Q2 2026) reframes who influences phosphate-lowering decisions. Nearly nine in ten renal dietitians say they have greater involvement than nephrologists in managing hyperphosphatemia. Nephrologists themselves corroborate that shift: in RealTime Dynamix™: Dialysis (US), Q4 2025, more than half reported that renal dietitians have significant influence over decisions to add or switch therapies.
Access pressures also shape dietitian recommendations. Approximately one-third report frequently recommending a different prescription because of patient out-of-pocket costs or insurance denials. Importantly, their treatment preferences diverge from physicians'. While dietitians most often favor Velphoro® (sucroferric oxyhydroxide, Fresenius Medical Care), nephrologists most often identify Xphozah as the therapy they would prefer to prescribe if access barriers were removed—though neither preference reaches a majority.
A Market That Misjudges How It Treats
Those physician attitudes, viewed alongside their reported behaviors in Patient Chart Dynamix™: Dialysis (US), reveal a meaningful perception gap. Spherix's audit of 1,033 dialysis patient charts found that one-third of treated patients remained above the historical phosphorus target at their most recent laboratory assessment, while nearly two-thirds exceeded target at least once during the previous six months.
Physicians, however, consistently overestimate both how well phosphorus is controlled and how aggressively uncontrolled patients are already being treated. Nephrologists estimate that roughly one-third of treated hyperphosphatemia patients receive combination therapy; chart data show the true figure is closer to one in seven.
This gap shows up at the patient level, too. When physicians say they'd be unlikely to prescribe Xphozah for a given patient, more than half call that patient 'well controlled.' But chart data tells a different story: one in eight of those 'well-controlled' patients were above target at their last phosphorus measurement. Physicians are missing chances to intensify therapy because they believe control is better than it is.
Xphozah Makes Gradual Inroads—but Faces Two Distinct Challenges
Nephrologists report Xphozah use has risen to approximately one in ten dialysis patients, and nearly two-thirds of current users began the therapy within six months of starting dialysis. Among all phosphate-lowering agents evaluated, Xphozah produced the largest reduction in serum phosphorus following initiation, consistent with its use in some of the most treatment-resistant patients. Physicians cite efficacy, lower pill burden, and its differentiated mechanism of action as the primary reasons for prescribing the therapy.
Persistence, however, presents a separate challenge. The proportion of patients who initiated and later discontinued Xphozah doubled over the past year, increasing from 4% to 8%, with gastrointestinal tolerability cited as the leading reason for discontinuation.
"Xphozah faces two distinct commercial challenges," said Kari McCarthy, Head of Nephrology at Spherix Global Insights. "Uptake remains constrained by formulary restrictions, prior authorization requirements, and by physicians who often believe patients are adequately controlled when many are not. Persistence, however, is limited by real-world gastrointestinal tolerability. One challenge is external to the product; the other reflects the treatment experience itself."
Why This Matters Now: Reimbursement Is Flattening the Field
The commercial importance of these findings will only increase as the reimbursement landscape changes. The six oral phosphate binders incorporated into the Medicare ESRD bundle in January 2025—including Velphoro®, Auryxia® (ferric citrate), Fosrenol® (lanthanum carbonate), Renvela®, Renagel®, and calcium acetate—are currently reimbursed through the Transitional Drug Add-on Payment Adjustment (TDAPA), which expires at the end of 2026. At that point, reimbursement will be absorbed into the dialysis bundled payment, reducing one of the key economic differentiators across the category.
Ardelyx's Xphozah entered the bundle on a different reimbursement pathway without TDAPA, but the market is ultimately moving toward the same destination: one in which reimbursement no longer meaningfully differentiates phosphate-lowering therapies.
Looking Ahead
Spherix's 2026 Patient Chart Dynamix™: Dialysis (US) study is currently fielding and will provide an updated view of whether physician treatment patterns, therapeutic escalation, and phosphate-lowering utilization begin to shift as the market transitions toward the post-TDAPA reimbursement environment.
About RealTime Dynamix™
RealTime Dynamix™ is an independent service providing strategic guidance through quarterly or semiannual reports, which include market trending and a fresh infusion of event-driven and variable content with each wave. The reports provide an unbiased view of the competitive landscape within rapidly evolving specialty markets, fueled by robust HCP primary research and our in-house team of experts.
About Patient Chart Dynamix™
Patient Chart Dynamix™ is an independent, data-driven service unveiling real patient management patterns through rigorous analysis of large-scale patient chart audits. Insights reveal the “why” behind treatment decisions, include year-over-year trending to quantify key aspects of market evolution, and integrate specialists’ attitudinal and demographic data to highlight differences between stated and actual treatment patterns.
About Spherix Global Insights
Spherix Global Insights is a leading independent provider of market intelligence and advisory services for specialty pharmaceutical and biotech markets. By combining physician, patient, and payer perspectives into a single integrated view, Spherix helps brand teams, market access stakeholders, and investors understand how a specialty market actually behaves, not how any one stakeholder describes it. The firm operates eight dedicated therapeutic franchises – Central Nervous System, Dermatology, Gastroenterology, Hematology, Nephrology, Oncology, Ophthalmology, and Rheumatology – alongside a fully dedicated Market Access team. Each franchise is led by hyper-focused analysts and researchers who track these specialty areas full-time, drawing on independently curated communities of vetted practicing specialists, KOLs, patients recruited through treating physicians and advocacy partners, and medical and pharmacy directors at commercial and government payers. Spherix delivers quarterly trending, launch tracking, chart audits, KOL synthesis, patient experience research, and payer and market access intelligence that support confident, strategic decision-making across the pharma lifecycle. Trusted by 19 of the top 20 pharmaceutical and biotech organizations, Spherix has been a go-to resource for more than a decade for leading brands, market access stakeholders, industry media outlets, financial analysts, professional organizations, and patient advocacy groups seeking an unbiased, holistic view of specialty markets.
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NOTICE: All company, brand or product names in this press release are trademarks of their respective holders. The findings and opinions expressed within are based on Spherix Global Insights’ analysis and do not imply a relationship with or endorsement of the companies or brands mentioned in this press release.
Kari McCarthy Spherix Global Insights 484-879-4284 kari.mccarthy@spherixglobalinights.com