A Potential New Treatment for the More Than 1.25 Million Americans Chronically
                     Infected with the Hepatitis B Virus
 
    COSTA MESA, Calif., Oct. 31 /PRNewswire-FirstCall/ -- Ribapharm Inc.
(NYSE: RNA) today announced that it has submitted an Investigational New Drug
(IND) application to the U.S. Food and Drug Administration (FDA) to initiate
Phase I clinical studies for Hepavir B in patients with chronic hepatitis B.
    "Ribapharm licensed the rights to develop and commercialize Hepavir B from
Metabasis Therapeutics Inc. in October 2001," said Johnson Y.N. Lau, MD,
President and CEO of Ribapharm.  "This filing, one year after securing the
rights to Hepavir B, underscores the commitment of the development team and
the strategic value of the partnership between Ribapharm and Metabasis."
    Metabasis discovered Hepavir B by applying its HepDirect(TM) prodrug
technology to a proven effective antiviral drug, PMEA.  The HepDirect(TM)
technology is a proprietary platform technology discovered and developed by
Metabasis. In animal studies, Hepavir B is predominately converted into the
active moiety in the liver.
    "Although Hepavir B is still in Preclinical Phase of development, it
represents an interesting prospect as the efficacy of the active compound,
PMEA, has been demonstrated to be active against both wild type and drug
resistant hepatitis B," said Robert Gish, MD, Director of Hepatology and Liver
Transplantation, California Pacific Medical Center, San Francisco.
    A Phase I clinical study on the safety of rising single doses of Hepavir B
in healthy volunteers was conducted in Europe in August 2002.  The study
showed that the incidence of treatment-emergent adverse events associated with
single oral doses of Hepavir B were 3 at 10 mg (6 subjects), 6 at 30 mg (12
subjects) and 0 at 60 mg (6 subjects) versus 5 with placebo (4 subjects),
indicating that single oral doses of Hepavir B up to 60 mg is comparable to
placebo in healthy adult volunteers.
 
    About Hepatitis B
    Hepatitis B is a viral infection of the liver.  The World Health
Organization (WHO) estimates that more than 350 million people worldwide have
chronic infections.  In the United States, the Centers for Disease Control and
Prevention (CDC) estimate nearly 78,000 people each year are newly infected
with hepatitis B.
    Chronic infection by the hepatitis B virus can lead to cirrhosis and liver
failure, as well as liver cancer in the more advanced stages of the disease.
The CDC estimates that death will occur in 15 to 25 percent of people
chronically infected with hepatitis B.
    Hepatitis B is highly infectious and occurs when blood or body fluids from
an infected person enters the body of a person who is not immune or
vaccinated.  The virus is often spread through sexual contact with an infected
person.  Contaminated needles used in intravenous drug injections and blood
transfusions from infected sources also spread the virus to otherwise healthy
individuals.  Hepatitis B infection can also be spread from mother to baby at
birth.
    Ribapharm is a biopharmaceutical company that seeks to discover, develop,
acquire and commercialize innovative products for the treatment of significant
unmet medical needs, principally in the antiviral and anticancer areas.
 
    THE "SAFE HARBOR" STATEMENT UNDER THE PRIVATE SECURITIES LITIGATION REFORM
ACT OF 1995.  This press release contains forward-looking statements that
involve risk and uncertainties, including but not limited to, projections of
future sales, operating income, returns on invested assets, regulatory
approval processes, and other risks detailed from time to time in the
Company's Securities and Exchange Commission filings.