Eiger BioPharmaceuticals Announces New HCV Synergy Data

Publication describes high level of synergy of clemizole with protease inhibitor class

PALO ALTO, California, July 1, 2010 - Eiger BioPharmaceuticals, Inc., a biotechnology company developing
antiviral therapies, announced today the publication of research from the lab
of Stanford scientist and Eiger Founder, Dr. Jeffrey Glenn, M.D., Ph.D. and
colleagues entitled, "The Hepatitis C Virus (HCV) NS4B RNA Binding Inhibitor
Clemizole is Highly Synergistic with HCV Protease Inhibitors".

"This work demonstrates that clemizole can yield high-level synergy with
the protease inhibitor class," said David Cory, President and CEO of Eiger.
"Inclusion of clemizole in future anti-HCV cocktails represents an attractive
paradigm for increasing virologic response rates and may minimize unwanted
side effects and combat drug resistance to HCV protease inhibitors."

"Clemizole appears to be able to dramatically increase the in vitro
efficacy of other agents such as the NS3 protease inhibitors in advanced
clinical development," said Jeffrey Glenn, M.D., Ph.D., Founder of Eiger.
"The addition of clemizole to regimens may allow protease inhibitors to be
used at lower doses, thereby maintaining the desired antiviral efficacy while
avoiding the toxicities associated with the protease inhibitors such as
severe rash and anemia. Clemizole has the potential to be an ideal component
of future anti-HCV cocktails."

About NS4B and Clemizole

Binding of the non-structural protein NS4B to the 3' terminus of the HCV
negative RNA strand is a recently identified target for drug intervention.
The requirement of this target for viral replication has been genetically
validated. The two component nature of this target, involving interaction
between NS4B and HCV-RNA, creates mutational constraints that should decrease
resistance to pharmacologic inhibitors, compared to agents designed against a
single component target such as the NS3 protease. Clemizole hydrochloride was
identified as a specific inhibitor of NS4B-RNA binding. The anti-HCV activity
of clemizole is currently being investigated across genotypes in multiple HCV
clinical proof of concept trials as a cocktail component with standard of
care medications.

About Eiger BioPharmaceuticals, Inc. www.eigerbio.com

Eiger is focused on the discovery and development of new antiviral agents
against novel targets for the treatment of hepatitis virus infections.
Eiger's pipeline includes repurposed clinical stage therapeutic agents as
well as preclinical NCEs from discovery that exhibit antiviral activity
against Hepatitis C, Hepatitis D, and other viruses. Eiger investors include
InterWest Partners www.interwest.com and Vivo Ventures
www.vivoventures.com.

Eiger BioPharmaceuticals, Inc., +1-650-320-9900, info at eigerbio.com