First Patient Dosed in ACCEL: Phase 3 Chronic Idiopathic Constipation Study of IBSRELA

Rhea-AI Summary

Ardelyx (Nasdaq: ARDX) announced the first patient has been dosed in ACCEL, a Phase 3 trial evaluating IBSRELA (tenapanor) for chronic idiopathic constipation (CIC).

ACCEL is randomized, double-blind, placebo-controlled, plans ~700 patients, twice-daily dosing for 26 weeks, enrollment through 2026 and topline data expected in H2 2027. Safety notes include diarrhea rates and a pediatric dehydration boxed warning.

Positive

• First patient dosed in Phase 3 ACCEL trial
• Planned enrollment ~700 patients for CIC study
• Topline data expected H2 2027, giving a clear timing milestone

Negative

• Diarrhea incidence 16% (IBSRELA) vs 4% (placebo)
• Severe diarrhea reported in 2.5% of treated patients
• Boxed warning: risk of serious dehydration in pediatric patients

Key Figures

ACCEL phase: Phase 3 Treatment duration: 26 weeks Planned enrollment: ≈700 patients +5 more

8 metrics

ACCEL phase Phase 3 ACCEL trial stage for IBSRELA in CIC

Treatment duration 26 weeks Twice-daily dosing period in ACCEL Phase 3 trial

Planned enrollment ≈700 patients Target sample size for ACCEL CIC study

CIC prevalence 34 million Americans Estimated chronic idiopathic constipation patient population

Severe diarrhea rate 2.5% Severe diarrhea in IBSRELA-treated IBS‑C patients

Diarrhea incidence 16% vs 4% Diarrhea in IBSRELA vs placebo in IBS‑C trials

Abdominal distension 3% vs <1% Abdominal distension in IBSRELA vs placebo

Flatulence rate 3% vs 1% Flatulence in IBSRELA vs placebo

Market Reality Check

Price: $7.86 Vol: Volume 2,818,791 is below...

low vol

$7.86 Last Close

Volume Volume 2,818,791 is below the 6,634,563 share 20-day average, suggesting a relatively muted participation ahead of this Phase 3 update. low

Technical Shares at $7.89 are above the $5.24 200-day MA and about 6% below the $8.40 52-week high.

Peers on Argus

ARDX gained 1.15% while close peers were mixed: gains in MNKD (+0.90%) and CDTX ...

ARDX gained 1.15% while close peers were mixed: gains in MNKD (+0.90%) and CDTX (+0.03%) contrasted with declines in AUPH (-0.68%), VCEL (-2.19%) and VERA (-1.79%). No peers appeared in the momentum scanner, supporting a stock-specific reaction.

Previous Clinical trial Reports

1 past event · Latest: Jul 31 (Positive)

Same Type Pattern 1 events

Date	Event	Sentiment	Move	Catalyst
Jul 31	Clinical data publication	Positive	+0.5%	Publication of plain language summaries from XPHOZAH clinical trials for CKD patients.

Pattern Detected

Clinical-trial–related communications have historically coincided with modest positive price reactions.

Recent Company History

Over the past six months, Ardelyx has highlighted strong commercial performance from IBSRELA and XPHOZAH, rising revenues, and multiple conference appearances. A prior July 31, 2024 clinical‑trial–related communication on XPHOZAH led to a modest 0.54% gain. The new ACCEL Phase 3 study for IBSRELA in chronic idiopathic constipation extends the company’s clinical footprint from kidney‑disease–focused tenapanor data toward broader GI indications, consistent with its strategy of expanding tenapanor’s reach.

Historical Comparison

clinical trial

+0.5 %

Average Historical Move

Historical Analysis

In the past, ARDX clinical‑trial communications produced modest moves, averaging 0.54%. Today’s 1.15% gain on the ACCEL Phase 3 initiation remains broadly consistent with that pattern.

Typical Pattern

Historical clinical‑trial communications centered on XPHOZAH’s dialysis population. The ACCEL Phase 3 study marks progression to a large, 26‑week tenapanor program in chronic idiopathic constipation, expanding beyond the earlier kidney‑focused trials.

Market Pulse Summary

This announcement details initiation of ACCEL, a Phase 3, ~700-patient study of IBSRELA in chronic i...

Analysis

This announcement details initiation of ACCEL, a Phase 3, ~700-patient study of IBSRELA in chronic idiopathic constipation with a 26‑week dosing period and topline data expected in the second half of 2027. It expands tenapanor’s clinical reach beyond IBS‑C into a CIC population estimated at over 34 million Americans. Investors may watch enrollment progress, safety outcomes such as diarrhea rates, and how this program fits alongside Ardelyx’s existing commercial indications.

Key Terms

chronic idiopathic constipation, randomized, double-blind, placebo-controlled, contraindications, adverse reactions, +1 more

5 terms

chronic idiopathic constipation medical

"for the treatment of chronic idiopathic constipation (CIC) in adults."

Chronic idiopathic constipation is a long-lasting condition where a person has infrequent or difficult bowel movements and no identifiable medical cause; “idiopathic” means doctors cannot find a specific underlying disease. It matters to investors because it represents a sizable, persistent patient population and a steady market for treatments, diagnostics and clinical trials—think of it as a common plumbing problem that creates ongoing demand for better tools and services.

randomized, double-blind, placebo-controlled medical

"a multicenter, randomized, double-blind, placebo-controlled study to assess the safety"

A "randomized, double-blind, placebo-controlled" process is a method used to test the effectiveness of a new treatment or intervention. Participants are randomly assigned to different groups, with one receiving the real treatment and the other a fake version, called a placebo. Neither the participants nor the researchers know who is receiving which, which helps ensure unbiased results. For investors, this rigorous approach increases confidence that the findings are accurate and not influenced by guesswork or bias.

contraindications medical

"CONTRAINDICATIONS IBSRELA is contraindicated in patients less than 6 years of age"

Contraindications are specific conditions, factors, or situations that make using a drug, device, or medical procedure unsafe or inadvisable for a particular person. For investors, contraindications are important because they limit how many patients can use a product and can affect regulatory labeling, sales forecasts and legal risk—think of them as built‑in “do not use” signs that narrow a product’s market.

adverse reactions medical

"MOST COMMON ADVERSE REACTIONS The most common adverse reactions in IBSRELA-treated"

Adverse reactions are harmful or unintended effects people experience after using a medicine, vaccine, medical device, or treatment; think of them as unexpected problems that show up when a product is used as intended. Investors care because these reactions can trigger regulatory warnings, safety reviews, recalls, reduced sales, or legal costs—similar to how widespread product defects can damage a company’s reputation and future earnings.

placebo medical

"diarrhea (16% vs 4% placebo), abdominal distension (3% vs <1%),"

A placebo is an inactive pill, injection or procedure that looks and feels like the real treatment but contains no therapeutic ingredient, often called a sugar pill. Investors care because comparing a drug to a placebo reveals whether observed benefits come from the medicine itself or from expectation; clear superiority over placebo reduces regulatory and commercial risk, much like a blind taste test proves a new recipe really tastes better.

AI-generated analysis. Not financial advice.

WALTHAM, Mass., Jan. 28, 2026 (GLOBE NEWSWIRE) -- Ardelyx, Inc. (Nasdaq: ARDX), a biopharmaceutical company founded with a mission to discover, develop and commercialize innovative, first-in-class medicines that meet significant unmet medical needs, today announced that the first patient has been dosed in ACCEL (ten-03-301), a Phase 3 clinical trial designed to assess the safety and efficacy of IBSRELA^® (tenapanor) for the treatment of chronic idiopathic constipation (CIC) in adults.

ACCEL is a multicenter, randomized, double-blind, placebo-controlled study to assess the safety and efficacy of tenapanor for the treatment of CIC in adults when administered twice daily for 26 consecutive weeks. The Phase 3 clinical trial is designed to enroll approximately 700 patients with CIC. The primary endpoint will evaluate patient-reported outcomes in constipation. Enrollment in ACCEL is expected throughout 2026, with topline data read out in the second half of 2027.

“Today marks an important milestone for our team and the patients we are committed to serving,” said Laura Williams, M.D., M.P.H, chief patient officer and interim chief medical officer of Ardelyx. “We are pleased to announce that the first patient has been dosed in the ACCEL Phase 3 clinical trial, an integral step to bringing IBSRELA and its differentiated mechanism of action to patients with chronic idiopathic constipation. This achievement reflects the dedication of our investigators, clinical staff, internal team, and most importantly, the patients and families who entrust us with their care. We remain focused on conducting this study with the highest standards of safety, integrity and scientific rigor, and we look forward to the insights it will provide for the future health of our patients.”

The Phase 3 ACCEL clinical trial represents important progress in Ardelyx’s goal of expanding the patient population who may benefit from IBSRELA, beyond its lead indication for irritable bowel syndrome with constipation, which demonstrated safety, efficacy and tolerability in a comprehensive clinical development plan.

CIC is characterized by difficult, infrequent or incomplete bowel movements, and is associated with significantly impaired quality of life, disrupted productivity and high healthcare-related costs. CIC is estimated to affect more than 34 million Americans¹.

IMPORTANT SAFETY INFORMATION (IBSRELA)

WARNING: RISK OF SERIOUS DEHYDRATION IN PEDIATRIC PATIENTS IBSRELA is contraindicated in patients less than 6 years of age; in nonclinical studies in young juvenile rats administration of tenapanor caused deaths presumed to be due to dehydration. Avoid use of IBSRELA in patients 6 years to less than 12 years of age. The safety and effectiveness of IBSRELA have not been established in patients less than 18 years of age.

CONTRAINDICATIONS

• IBSRELA is contraindicated in patients less than 6 years of age due to the risk of serious dehydration.
• IBSRELA is contraindicated in patients with known or suspected mechanical gastrointestinal obstruction.

WARNINGS AND PRECAUTIONS
Risk of Serious Dehydration in Pediatric Patients

• IBSRELA is contraindicated in patients below 6 years of age. The safety and effectiveness of IBSRELA in patients less than 18 years of age have not been established. In young juvenile rats (less than 1 week old; approximate human age equivalent of less than 2 years of age), decreased body weight and deaths occurred, presumed to be due to dehydration, following oral administration of tenapanor. There are no data available in older juvenile rats (human age equivalent 2 years to less than 12 years).
• Avoid the use of IBSRELA in patients 6 years to less than 12 years of age. Although there are no data in older juvenile rats, given the deaths in younger rats and the lack of clinical safety and efficacy data in pediatric patients, avoid the use of IBSRELA in patients 6 years to less than 12 years of age.

Diarrhea
Diarrhea was the most common adverse reaction in two randomized, double-blind, placebo-controlled trials of IBS-C. Severe diarrhea was reported in 2.5% of IBSRELA-treated patients. If severe diarrhea occurs, suspend dosing and rehydrate patient.

MOST COMMON ADVERSE REACTIONS
The most common adverse reactions in IBSRELA-treated patients (incidence ≥2% and greater than placebo) were: diarrhea (16% vs 4% placebo), abdominal distension (3% vs <1%), flatulence (3% vs 1%) and dizziness (2% vs <1%).

INDICATION
IBSRELA (tenapanor) is indicated for the treatment of Irritable Bowel Syndrome with Constipation (IBS-C) in adults.

Please see full Prescribing Information, including Boxed Warning, for additional risk information.

About Ardelyx
Ardelyx was founded with a mission to discover, develop and commercialize innovative, first-in-class medicines that meet significant unmet medical needs. Ardelyx has two commercial products approved in the United States, IBSRELA® (tenapanor) and XPHOZAH® (tenapanor). The company’s pipeline includes the Phase 3 development of IBSRELA for chronic idiopathic constipation (CIC) and RDX10531, a next-generation NHE3 inhibitor with potential application across multiple therapeutic areas. Ardelyx has agreements for the development and commercialization of tenapanor outside of the U.S. Kyowa Kirin commercializes PHOZEVEL^® (tenapanor) for hyperphosphatemia in Japan. A New Drug Application for tenapanor for hyperphosphatemia has been approved in China with Fosun Pharma. Knight Therapeutics commercializes IBSRELA in Canada. For more information, please visit https://ardelyx.com/ and connect with us on X (formerly known as Twitter), LinkedIn and Facebook.

Forward Looking Statements
To the extent that statements contained in this press release are not descriptions of historical facts regarding Ardelyx, they are forward-looking statements reflecting the current beliefs and expectations of management made pursuant to the safe harbor of the Private Securities Litigation Reform Act of 1995. Forward-looking statements include, but are not limited to, Ardelyx’s current expectations regarding the timing for completion of enrollment of the CIC Phase 3 clinical trial; the timing for the release of topline data from the CIC Phase 3 clinical trial; and the expansion of the patient population who may benefit from IBSRELA. Such forward-looking statements involve known and unknown risks, uncertainties and other factors that are in some cases beyond our control, that could cause actual outcomes or results to differ materially from those expressed or implied by the forward-looking statements. Such risks and uncertainties include, among others, risks related to clinical development and regulatory approval; commercialization, market acceptance and payer coverage. Ardelyx undertakes no obligation to update or revise any forward-looking statements, except as required by law. For a further description of the risks and uncertainties that could cause actual results to differ from those expressed in these forward-looking statements, as well as risks relating to Ardelyx's business in general, please refer to Ardelyx's Quarterly Report on Form 10-Q filed with the Securities and Exchange Commission on October 30, 2025, and its future current and periodic reports to be filed with the Securities and Exchange Commission.

Investor and Media Contacts:
Caitlin Lowie
clowie@ardelyx.com

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¹ NIH: CIC affects about 10-17% of the world population. https://pmc.ncbi.nlm.nih.gov/articles/PMC8547593/ Current U.S. population as of Dec 7, 2025 (https://www.census.gov/popclock/): 342,939,118. 10% of U.S. Population: 34,293,911.

FAQ

What is the ACCEL Phase 3 trial for IBSRELA (ARDX) testing?

ACCEL tests IBSRELA (tenapanor) for chronic idiopathic constipation in adults. According to the company, the randomized, double-blind, placebo-controlled study assesses safety and efficacy with twice-daily dosing for 26 weeks in about 700 patients.

When will ACCEL (ARDX) complete enrollment and report topline data?

Enrollment in ACCEL is expected throughout 2026, with topline results in the second half of 2027. According to the company, the study plans to enroll approximately 700 patients with CIC and run 26-week treatment periods.

How long will patients receive IBSRELA in the ACCEL trial (ARDX)?

Patients will receive IBSRELA twice daily for 26 consecutive weeks. According to the company, the design evaluates patient-reported constipation outcomes over the six-month treatment period to assess safety and efficacy.

What safety risks are highlighted for IBSRELA (ARDX) in the ACCEL announcement?

Diarrhea was the most common adverse reaction, 16% versus 4% with placebo, with severe diarrhea in 2.5% of treated patients. According to the company, there is a boxed warning for pediatric dehydration and contraindication in young children.

How does ACCEL expand IBSRELA's potential patient population for ARDX?

ACCEL evaluates IBSRELA for chronic idiopathic constipation, extending use beyond irritable bowel syndrome with constipation. According to the company, the Phase 3 aims to determine safety and efficacy in a broader adult CIC population of roughly 700 patients.