Hepavir B

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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.