Hyperion Therapeutics Announces RAVICTI and BUPHENYL Pharmacokinetic Analyses Reported in The Journal of Clinical Pharmacology

Hyperion Therapeutics Announces RAVICTI and BUPHENYL Pharmacokinetic Analyses
Reported in The Journal of Clinical Pharmacology

SOUTH SAN FRANCISCO, Calif., June 18, 2013 (GLOBE NEWSWIRE) -- Hyperion
Therapeutics, Inc. (Nasdaq:HPTX) today announced that population
pharmacokinetic (PK) modeling and dosing simulations were reported in The
Journal of Clinical Pharmacology based on data from four Phase 2 and 3 trials
that collectively enrolled patients with urea cycle disorders (UCDs) ages 2
months to 72 years. The final model described the differences in absorption
rate and pharmacokinetic profiles of the company's two drugs, RAVICTI®
(glycerol phenylbutyrate) Oral Liquid and BUPHENYL® (sodium phenylbutyrate)
Tablets and Powder, in patients with UCDs. The article is available through
the Wiley online library

UCDsrepresent a collection of inherited enzyme and transporter deficiencies
that impair the synthesis of urea, the body's vehicle for waste nitrogen
removal via the urine, which results in affected patients suffering from high
systemic levels of ammonia, a potent neurotoxin.Since UCDs constitute an
ultra-orphan population with an estimated U.S. patient pool of approximately
1000, population PK modeling and dosing simulations were performed to help
define the clinical pharmacology of the two compounds as well as metabolite
exposure in pediatric and adult UCD patients.

The final model helps explain differences in the level of plasma metabolites
(drug breakdown products) during dosing of the two drugsbased on differences
in the amount of drug metabolized tophenylacetylglutamine prior to reaching
the systemic circulation. Moreover, during dosing with RAVICTI as compared
with BUPHENYL, phenylbutyric acid is absorbed 70-75% more slowly and blood
metabolite levels generally show less fluctuation.

"These modeling data are particularly interesting in that the slower input of
the active ingredient into the circulation with RAVICTI as compared with the
bolus type drug release of BUPHENYL may allow for more sustained ammonia
control," said Dr. George Diaz, Associate Professor,Department of Genetics &
Genomic Sciences, Mount Sinai School of Medicine.

Bruce Scharschmidt, MD, Hyperion's chief medical officer added, "This work
represents an outstanding example of how population PK modeling and dosing
simulations can be used to help understand the behavior of drugs for patients
with rare diseases in which large trials are not feasible. We are pleased to
provide the UCD community with options to treat this serious
disease.Specifically, with our launch of RAVICTI earlier this year, patients
now have access to an important new option."

BUPHENYL tablet daily dosing requirements may be as much as 40 tablets per day
while the maximum daily dose for newly-approved RAVICTI is approximately three

About BUPHENYL (sodium phenylbutyrate) Tablets and Powder

BUPHENYL 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 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 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.

Please see full Prescribing Information for BUPHENYL at

RAVICTI Safety Information

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)

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. For more information, please
visit www.hyperiontx.com.

CONTACT: Sylvia Wheeler
         Vice President, Investor Relations
         (650) 745-7834
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