METABASIS REPORTS THE EARNING OF A MILESTONE PAYMENT BASED ON CONTINUED DEVELOPMENT OF REMOFOVIR FOR THE TREATMENT OF HEPATITIS B

SAN DIEGO, CA - April 16, 2004 --
Metabasis Therapeutics, Inc. (Metabasis) announced today that Valeant Pharmaceuticals International has agreed to pay a $1 million milestone payment to Metabasis in recognition of a decision to initiate a Phase II clinical evaluation of remofovir (formerly known as Hepavir B) in patients with chronic hepatitis B infection. Valeant licensed remofovir, an orally active prodrug of the proven antiviral agent adefovir, from Metabasis in October 2001 and is primarily responsible for the clinical development of the drug. The decision to proceed with development was based on results recently obtained from the first clinical evaluation of remofovir in patients infected with the hepatitis B virus.

About Metabasis
Metabasis Therapeutics, Inc. (www.mbasis.com) is a biopharmaceutical company focused on the discovery, development and commercialization of novel small molecule drugs principally to treat liver diseases and metabolic diseases linked to pathways in the liver. The company has established a broad product pipeline targeting large markets with significant unmet medical needs. Metabasis currently has three internally discovered product candidates in clinical trials indicated for the treatment of type 2 diabetes, hepatitis B and primary liver cancer.