February 25, 2014

Hyperion Therapeutics Announces the Publication of Phase 2 Results of Glycerol Phenylbutyrate (GPB) for the Treatment of Hepatic Encephalopathy in Hepatology

Data Show Significant Reduction in HE Events and Trend Toward Fewer Hospitalizations in GPB Treated Patients

BRISBANE, Calif., Feb. 25, 2014 (GLOBE NEWSWIRE) -- Hyperion Therapeutics, Inc. (Nasdaq:HPTX) today announced that results of the Phase 2 trial of glycerol phenylbutyrate (GPB) for the treatment of hepatic encephalopathy (HE) were published in the March 2014 issue of Hepatology. The study met its primary endpoint with significantly fewer patients treated with GPB experiencing HE events as compared to patients receiving placebo.

The randomized, double-blind, placebo-controlled Phase 2 trial enrolled 178 patients with cirrhosis, including 59 already taking rifaximin, who had experienced two or more HE events in the prior six months. Patients were randomized in a 1:1 ratio to receive 6 mL GPB or placebo, orally, twice daily for 16 weeks. The primary endpoint was the proportion of patients with HE events. GPB significantly reduced the proportion of patients who experienced a HE event (21% compared to 36%, p=0.02), as well as the time to first HE event (hazard ratio = 0.56, p < 0.05) and total HE events (35 versus 57, p=0.04) and was associated with fewer HE hospitalizations (13 versus 25, p=0.06). Among the subgroup of patients not taking rifaximin at baseline, there was a highly statistically significant reduction among patients randomized to GPB both in the percentage of patients with events (10% versus 32%; p < 0.01) and the total number of HE events (7 versus 31; p < 0.001). Among patients taking rifaximin at baseline, there was no difference in the proportion of patients with events or total events, although a non-significant trend was observed with respect to fewer hospitalizations in patients randomized to GPB. A similar proportion of patients in the GPB (79%) and placebo group (76%) experienced adverse events.

"We and our investigators are gratified by the results and new information the trial has yielded regarding the importance of ammonia in the pathogenesis of HE. We look forward to initiating enrollment in our pivotal Phase 3 trial late this year or early 2015 with the ultimate goal of providing HE patients with a new therapeutic alternative," said Bruce Scharschmidt, M.D., chief medical officer at Hyperion.

About Hepatic Encephalopathy

HE is a serious but potentially reversible neurological disorder that can occur in patients with cirrhosis of any etiology or acute liver failure. HE comprises a spectrum of neurological signs and symptoms ranging from mild (e.g. minimal disorientation) to severe (e.g. coma, death) and is believed to occur when the brain is exposed to gut-derived toxins such as ammonia that are normally removed from the blood by a healthy liver. Based on the current epidemiological data, Hyperion estimates that approximately 140,000 cirrhosis patients have overt HE.

About Glycerol Phenylbutyrate

Glycerol phenylbutyrate, is a pre-pro-drug of phenylacetic acid, the active moiety of RAVICTI® and BUPHENYL®, branded therapies currently FDA-approved as adjunctive therapy for the chronic management of patients with the most prevalent urea cycle disorders. Glycerol phenylbutyrate holds orphan product exclusivity in the United States and orphan designation in Europe for the maintenance treatment of patients with urea cycle disorders (UCD) and in the United States for the intermittent or chronic treatment of patients with cirrhosis and any grade of hepatic encephalopathy.

RAVICTI is indicated for use as a nitrogen binding agent for chronic management of adult and pediatric patients ≥2 years of age with UCDs who cannot be managed by dietary protein restriction and/or amino acid supplementation alone. RAVICTI must be used with dietary protein restriction and, in some cases, dietary supplements (e.g., essential amino acids, arginine, citrulline, protein-free calorie supplements). RAVICTI is not indicated for the treatment of acute hyperammonemia in patients with UCDs because more rapidly acting interventions are essential to reduce plasma ammonia levels. The safety and efficacy of RAVICTI for the treatment of N-acetylglutamate synthase (NAGS) deficiency has not been established. The use of RAVICTI in patients < 2 months of age is contraindicated. For additional Important Safety Information, including Warnings and Precautions, Adverse Events, Drug Interactions, and Special Populations, please see full Prescribing Information http://www.ravicti.com/files/RAVICTI_Prescribing_Information.pdf) and Medication Guide (http://www.ravicti.com/files/RAVICTI_Medication_Guide.pdf) for RAVICTI.

About Hyperion Therapeutics

Hyperion Therapeutics, Inc. is a commercial stage biopharmaceutical company committed to developing and delivering life-changing treatments for orphan diseases and hepatology. The company's first commercial product, RAVICTI® (glycerol phenylbutyrate) Oral Liquid, was approved in February 2013 and is currently being marketed in the United States. The company also owns worldwide rights to BUPHENYL® (sodium phenylbutyrate) Tablets and Powder which it markets in the U.S. The compound is also marketed in ex-U.S. geographies through business partners. For more information, please visit www.hyperiontx.com.

Forward-Looking Statements

To the extent that statements contained in this press release are not descriptions of historical facts regarding Hyperion, they are forward-looking statements reflecting the current beliefs and expectations of management made pursuant to the safe harbor provisions of the Private Securities Litigation Reform Act of 1995. Words such as "may," "will," "expect," "anticipate," "estimate," "intend," and similar expressions (as well as other words or expressions referencing future events, conditions or circumstances) are intended to identify forward-looking statements. Forward-looking statements contained in this press release include expectations about future cost of sales for RAVICTI and BUPHENYL. Hyperion undertakes no obligation to update or revise any forward-looking statements. For a further description of the risks and uncertainties relating to the business of the company in general, see Hyperion's most recent Quarterly Report on Form 10-Q filed with the Securities and Exchange Commission and any subsequent filings with the Securities and Exchange Commission.

CONTACT: Sylvia Wheeler

         Vice President, Investor Relations

         (650) 745-7834
Source: Hyperion Therapeutics, Inc.

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