BioCryst Provides Update Regarding BCX5191 Development Plan Following Discussion With FDA

  BioCryst Provides Update Regarding BCX5191 Development Plan Following
  Discussion With FDA

Business Wire

RESEARCH TRIANGLE PARK, N.C. -- October 30, 2012

BioCryst Pharmaceuticals, Inc. (NASDAQ:BCRX) today announced the withdrawal of
its Investigational New Drug application (IND) for the antiviral nucleoside,
BCX5191, following a discussion with the U.S. Food and Drug Administration
(FDA).

The FDA indicated concerns regarding the preclinical toxicity profile of
BCX5191 at exposure levels that they believe are likely to be necessary to
reduce viral load in patients infected with the hepatitis C virus (HCV).
Patient safety remains BioCryst’s highest priority. BioCryst continues to
believe that BCX5191 may be distinct from other Nucs in exhibiting antiviral
potency in man at significantly lower doses than other Nucs in development
based on preclinical results, and will therefore conduct additional
preclinical studies to determine if low doses—i.e. doses that are not
associated with toxicity in animals—exhibit meaningful viral load reductions
in HCV infected animals. BioCryst will then determine whether to continue
development of BCX5191, based on the results of these studies.

BioCryst agrees with the FDA’s cautious approach to the development of
nucleoside and nucleotide inhibitors for HCV. Further, BioCryst believes that
the recent occurrence of serious adverse events in HCV patients treated with
BMS-986094, a nucleotide prodrug previously under clinical development by
Bristol-Myers Squibb, has heightened safety concerns regarding this class of
HCV inhibitors. FDA has previously placed clinical holds on other nucleotides
under development.

About BCX5191

Discovered by BioCryst, BCX5191 is a novel, oral, pan-genotypic adenine
nucleoside analog targeting viral RNA polymerase for the potential treatment
of patients with HCV. BCX5191 inhibits the viral RNA polymerase enzyme across
genotypes 1-4 at sub-micromolar concentrations and it is active in replicon
cell assays. In human liver cells, BCX5191 rapidly and efficiently converts
into its active triphosphate form. In preclinical models, BCX5191 demonstrates
high oral bioavailability and is actively transported into the liver, without
requiring prodrug technology. PK modeling supports once-daily dosing in
clinical studies and predicts that low doses of BCX5191 will show antiviral
activity.

About Hepatitis C

Hepatitis C is a contagious liver disease that results from infection with the
hepatitis C virus (HCV), which is the most common virus that infects the liver
and can lead to life-threatening liver problems, such as liver damage,
cirrhosis, liver failure or liver cancer. There are an estimated 170 million
individuals worldwide who are chronically infected with HCV, and about 3 to 4
million people are infected annually. In the United States, there are
approximately 4 million people who have chronic hepatitis C.

Conference Call and Webcast

BioCryst's leadership team will host a conference call and webcast Wednesday,
October 31, 2012 at 8:30 a.m. Eastern Time. To participate in the conference
call, please dial 1-877-303-8027 (United States) or 1-760-536-5165
(International). No passcode is needed for the call. The webcast can be
accessed by logging onto www.BioCryst.com. Please connect to the website at
least 15 minutes prior to the start of the conference call to ensure adequate
time for any software download that may be necessary.

About BioCryst

BioCryst Pharmaceuticals designs, optimizes and develops novel small molecule
drugs that block key enzymes involved in infectious and inflammatory diseases.
BioCryst currently has two late-stage development programs: peramivir, a viral
neuraminidase inhibitor for the treatment of influenza, and ulodesine
(BCX4208), a purine nucleoside phosphorylase (PNP) inhibitor for the treatment
of gout. In addition, BioCryst is advancing two preclinical programs: BCX5191,
a nucleoside analog inhibitor of HCV RNA polymerase (NS5B) for hepatitis C,
and BCX4161, an oral inhibitor of plasma kallikrein for hereditary angioedema.
Utilizing state-of-the-art structure-guided drug design and crystallography,
BioCryst continues to discover innovative compounds with the goal of
addressing unmet medical needs of patients and physicians. For more
information, please visit the Company's website at www.BioCryst.com.

About the BioCryst-Presidio Merger

BioCryst and privately held Presidio Pharmaceuticals, Inc. recently announced
the signing of a definitive merger agreement to create a focused, clinical
stage biopharmaceutical company with lead programs in high-value infectious
and orphan disease indications: specifically HCV and hereditary angioedema
(HAE).

Important Additional Information and Where to Find It

BioCryst intends to file with the Securities and Exchange Commission (“SEC”) a
registration statement on Form S-4, which will also include a proxy statement
and prospectus with respect to its proposed acquisition of Presidio. The final
proxy statement/prospectus will be mailed to the stockholders of BioCryst and
Presidio. Investors and security holders are urged to read the proxy
statement/prospectus regarding the proposed transaction carefully and in its
entirety when it becomes available because it will contain important
information regarding BioCryst, Presidio and the proposed merger. Investors
will be able to obtain a free copy of the proxy statement/prospectus, as well
as other filings containing information about BioCryst, without charge, at the
SEC’s website (http://www.sec.gov/). Investors may also obtain these
documents, without charge, from BioCryst’s website at
http://investor.shareholder.com/biocryst/sec.cfm.

This communication shall not constitute an offer to sell or the solicitation
of an offer to buy any securities in the equity financing connected to the
proposed acquisition of Presidio.

Participants in the Merger Solicitation

BioCryst and its directors, executive officers and other members of management
and employees may be deemed to be participants in the solicitation of proxies
from shareholders with respect to the transactions contemplated by the
definitive merger agreement signed by Presidio. Information regarding
BioCryst’s directors and executive officers is contained in BioCryst’s 2011
Annual Report on Form 10-K filed with the SEC on March 6, 2012 and its
definitive proxy statement filed with the SEC on April 9, 2012 in connection
with its 2012 meeting of stockholders. Other information regarding the
participants in the proxy solicitation and a description of their direct and
indirect interests, by security holdings or otherwise, will be contained in
the proxy statement/prospectus and other relevant materials to be filed with
the SEC when they become available.

Forward-Looking Statements

This press release contains forward-looking statements, including statements
regarding future results, performance or achievements. These statements
involve known and unknown risks, uncertainties and other factors which may
cause BioCryst’s actual results, performance or achievements to be materially
different from any future results, performances or achievements expressed or
implied by the forward-looking statements. These statements reflect our
current views with respect to future events and are based on assumptions and
subject to risks and uncertainties. Given these uncertainties, you should not
place undue reliance on these forward-looking statements. Some of the factors
that could affect the forward-looking statements contained herein include:
that the FDA may require additional studies beyond the studies planned for
product candidates or may not provide regulatory clearances (e.g. BCX5191)
which may result in delay of planned clinical trials, clinical hold with
respect to such product candidate or inability to move forward with
development or the lack of market approval for such product candidate; that
ongoing and future preclinical and clinical development may not have positive
results; that the company or licensees may not be able to continue future
development of current and future development programs; that such development
programs may never result in future product, license or royalty payments being
received; that the company may not be able to retain its current
pharmaceutical and biotechnology partners for further development of its
product candidates or may not reach favorable agreements with potential
pharmaceutical and biotechnology partners for further development of product
candidates; that actual cash burn rate may not be consistent with
expectations; that the peramivir interim analysis may not be favorable or that
BARDA/HHS may further condition, reduce or eliminate future funding of the
peramivir program; that the planned merger with Presidio might not be
completed for any number of reasons, most of which are outside of the control
of BioCryst; that BioCryst may not be able to obtain the requisite financing
to complete the planned merger with Presidio on commercially reasonable terms
or that or that the financing may be raised at prices below the currently
prevailing price for BioCryst common stock; that integration of BioCryst and
Presidio may prove more challenging than anticipated or that anticipated
benefits of the merger may not be achieved, or may be achieved less rapidly
than anticipated; the outcome of any legal proceedings that may be instituted
against BioCryst or Presidio; risks relating to any unforeseen liabilities,
future capital expenditures, revenues, expenses, earnings, economic
performance, indebtedness, financial condition, losses and future prospects,
business and management strategies or the expansion and growth of Presidio’s
operations; BioCryst’s ability to integrate Presidio’s business successfully
after the closing of the merger agreement; and the risk that disruptions from
the merger agreement will harm BioCryst’s or Presidio’s businesses. There can
be no assurance that the proposed merger and financing will in fact be
consummated. Other important factors include: that there can be no assurance
that BioCryst’s or Presidio’s compounds will prove effective in clinical
trials; that development and commercialization of BioCryst’s or Presidio’s
compounds may not be successful; that BioCryst, Presidio or licensees may not
be able to enroll the required number of subjects in planned clinical trials
of its product candidates and that such clinical trials may not be
successfully completed; that the companies or licensees may not commence as
expected additional human clinical trials with product candidates; that 2012
operating expenses and cash usage will be within management’s expected ranges;
that BioCryst or Presidio may not have sufficient cash to continue funding the
development, manufacturing, marketing or distribution of products and that
additional funding, if necessary, may not be available at all or on terms
acceptable to BioCryst or Presidio. Please refer to the documents BioCryst
files periodically with the Securities and Exchange Commission, specifically
BioCryst's most recent Annual Report on Form 10-K, Quarterly Reports on Form
10-Q, and current reports on Form 8-K, all of which identify important factors
that could cause the actual results to differ materially from those contained
in BioCryst’s projections and forward-looking statements.

BCRXW

Contact:

BioCryst Pharmaceuticals
Robert Bennett, 919-859-7910 (investors)
or
WCG
Catherine Kyroulis, 212-301-7174 (Media)