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

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)."

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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.

About BUPHENYL(R)
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 www.hyperiontx.com.

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 www.Buphenyl.com
or by contacting Ucyclyd Pharma, Inc.

SOURCE Hyperion Therapeutics, Inc.

Christine Nash of Hyperion Therapeutics, Inc., +1-650-745-7844