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Hyperion Therapeutics Announces Results for Phase II Study in Urea Cycle Disorders

- Company preparing to initiate phase III trial -

SOUTH SAN FRANCISCO, Calif., March 30 /PRNewswire/ -- Hyperion Therapeutics, Inc. today announced top-line results from their phase II study of HPN-100 for the treatment of urea cycle disorders. The data was presented on March 27th at the 16th Annual Clinical Genetics Meeting of the American College of Medical Genetics by Brendan Lee, M.D., Ph.D., Howard Hughes Medical Institute Investigator and Professor Department of Molecular and Human Genetics Baylor College of Medicine. The abstract is entitled "Phase 2 Study of A Novel Ammonia Scavenging Agent In Adults With Urea Cycle Disorders (UCDs)."


The phase II study was an open-label, fixed sequence, switch-over study [BUPHENYL(R) (sodium phenylbutyrate) to HPN-100] of ten adult subjects with UCDs. The primary endpoint was safety; secondary outcome measures included pharmacokinetics (PK), pharmacodynamics (PD), and exploratory efficacy as measured by time-normalized area under the curve (TNAUC) for ammonia. Patients were enrolled on their stable dose of BUPHENYL and 24-hour PK, ammonia measurements, amino acids, and urine collections were completed in a study unit after seven days of on-study treatment. Each patient was then switched to HPN-100 at a dose providing the same amount of the active ingredient (PBA). After seven days of HPN-100 dosing, patients were re-admitted for the same battery of assessments that were completed at day seven. Both BUPHENYL and HPN-100 were administered TID with meals.

Twenty-one adverse events (AEs) occurred in seven subjects during BUPHENYL treatment and fifteen AEs occurred in five subjects with HPN-100. There were two SAEs related to hyperammonemia; both occurred during 100% BUPHENYL treatment. No SAEs occurred during 100% HPN-100 treatment. Ammonia values were ~30% lower on HPN-100 assessed as TNAUC over 24 hours [mean (SD) = 38.4 (19.6) versus 26.1 (10.3) umol/L), Cmax = 79.1 (40.1) versus 56.3 (27.9) umol/L, or the percentage of normal values: 58% vs. 72%]. Differences in ammonia values were not statistically significant.

"We are very pleased with the study results and our recent end of phase II meeting with the Food and Drug Administration," said Don Santel, Chief Executive Officer of Hyperion Therapeutics. "We are currently finalizing our phase III study protocol in consultation with the Agency and are eager to further explore the potential of HPN-100 for the treatment of urea cycle disorders."

About Urea Cycle Disorders

Urea cycle disorders are inherited, inborn errors of metabolism present in an estimated 1 in 10,000 births in the United States. Patients with urea cycle disorders are deficient in one of the key enzymes that comprise the urea cycle, the body's primary vehicle for removing ammonia, a potent neurotoxin, from the bloodstream. Onset may occur at any age depending on the severity of the disorder. Left untreated, urea cycle disorders can cause dangerously heightened levels of ammonia in the bloodstream (hyperammonemia) resulting in brain damage, coma, and/or death.

About HPN-100

HPN-100 is a pro-drug of phenylbutyrate and a pre-pro-drug of phenylacetic acid, the active moiety of BUPHENYL(R), the only therapy currently FDA-approved as adjunctive therapy for the chronic management of patients with the most prevalent urea cycle deficiencies including those related to carbamylphosphate synthetase, ornithine transcarbamylase and argininosuccinic acid synthetase. HPN-100, which is dosed orally in liquid form, provides an alternative pathway to the urea cycle for the disposal of waste nitrogen through the renal excretion of phenylacetylglutamine, which is formed from phenylacetic acid and glutamine.

Hyperion and Ucyclyd Pharma, Inc., a subsidiary of Medicis Pharmaceutical Corporation, entered into a collaboration agreement for HPN-100 in August 2007. Under the terms of the agreement, Hyperion is conducting ongoing research and development of HPN-100 for urea cycle disorders, hepatic encephalopathy, and other forms of hyperammonemia.


BUPHENYL(R) is indicated as adjunctive therapy in the chronic management of patients with urea cycle disorders involving deficiencies of carbamylphosphate synthetase (CPS), ornithine transcarbamylase (OTC), or argininosuccinic acid synthetase (AS). BUPHENYL(R) should not be administered to patients with known hypersensitivity to sodium phenylbutyrate or any component of this preparation. The most common adverse reactions associated with BUPHENYL(R) were amenorrhea dysfunction, decreased appetite, body odor (probably caused by its metabolite phenylacetate) and bad taste or taste aversion. Patients with urea cycle disorders should not take valproic acid, haloperidol, or steroids as these drugs have been reported to increase blood ammonia levels, and probenecid may affect the kidneys' excretion. Use with great care, if at all, in patients with congestive heart failure or severe renal insufficiency, and in clinical states where there is sodium retention with edema. Use caution when administering to patients with hepatic or renal insufficiency or inborn errors of beta oxidation. The safety or efficacy of doses in excess of 20 grams (40 tablets) per day has not been established.

About Hyperion Therapeutics

Hyperion Therapeutics is a privately held specialty therapeutics company focused on the development of therapies that address critical unmet needs and underserved patient populations in the areas of gastroenterology and hepatology. Hyperion is headquartered in South San Francisco, CA. For additional information, visit

BUPHENYL(R) is exclusively licensed from Ucyclyd Pharma, Inc.

BUPHENYL(R) is a registered trademark of Ucyclyd Pharma, Inc.

Full Prescribing Information for BUPHENYL(R) is available at or by contacting Ucyclyd Pharma, Inc.

SOURCE Hyperion Therapeutics, Inc.
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