METABASIS THERAPEUTICS, INC. ANNOUNCES RECEIPT OF A MILESTONE PAYMENT AFTER COMPLETION OF A SUCCESSFUL PHASE IIA STUDY OF CS-917, A DRUG TO TREAT TYPE 2 DIABETES MELLITUS

SAN DIEGO, CA - April 8, 2004 --
Metabasis Therapeutics, Inc. announced today that it has received a milestone payment of $3.5 million from Sankyo Co., Ltd. (Sankyo) for the successful completion of a second Phase IIA trial on CS-917, its first-in-class oral gluconeogenesis inhibitor for the treatment of patients with type 2 diabetes mellitus (diabetes). The study explored the effect of multiple daily dosing over a 28-day period on fasting glucose measured in the morning prior to drug administration. The results provide evidence that this new class of drugs is capable of significantly reducing blood glucose levels in patients with diabetes. Sankyo, Metabasis' partner on the project, has responsibility for funding and directing the clinical development of the drug.

The Phase IIA study was a randomized, placebo controlled, double blind, 28 day trial involving 144 patients with type 2 diabetes. Patients were randomized into four groups. One group received a placebo, the second and third groups received two different doses of CS-917 administered twice a day and the fourth group received CS-917 administered three times per day. All three groups that received CS-917 exhibited statistically significant improvement in the protocol specified endpoint of change from baseline in fasting morning plasma glucose levels on day 29 relative to placebo-treated patients.

Dr. Paul Laikind, Chairman, CEO and President at Metabasis stated, "We are very pleased with Sankyo's progress with CS-917. The study just completed represents an important proof of concept and builds on our earlier finding. Of course, larger studies involving longer treatment periods are required before we can demonstrate that the drug will be a safe and effective treatment for patients with type 2 diabetes."

According to the American Diabetes Association, as of 2002 approximately 17 million people in the United States had diabetes. Approximately 90% of Americans who are diagnosed with diabetes have type 2 diabetes. The number of new cases of diabetes is rising rapidly. Based on estimates by the World Health Organization, type 2 diabetes afflicted approximately 159 million people worldwide in 2000 and will afflict approximately 333 million people worldwide by 2030.

About Metabasis:

Metabasis Therapeutics, Inc. (www.mbasis.com) is a privately held, biopharmaceutical company that develops proprietary products principally for the treatment of liver and liver-related metabolic diseases. Metabasis has expertise in the fields of nucleoside/nucleotide chemistry and metabolism, liver biology and liver-specific drug delivery. Metabasis has discovered and developed a new class of drug candidates for treating diabetes that act to lower liver glucose production in diabetic patients. The first drug candidate from this program, CS-917, is being developed in collaboration with Sankyo Co., Ltd. and is currently undergoing clinical testing. Metabasis has also developed its HepDirect technology that allows liver-specific delivery of new and existing drugs. Two novel drug candidates derived from the HepDirect technology are in clinical testing: a drug for hepatitis B called remofovir (formerly called Hepavir B), developed in collaboration with Valeant Pharmaceuticals International and a drug for primary liver cancer called MB07133, to which Metabasis retains exclusive rights.

About Sankyo:
Sankyo Co., Ltd. is one of Japan's largest pharmaceutical companies with worldwide annual sales of $5 billion. Sankyo has a long history of discovering new classes of drugs, including the statin class of lipid-lowering drugs, with its discovery of the first statin, which was mevastatin (compactin, ML236B). Sankyo also discovered, co-developed and manufactures pravastatin sodium. Currently Sankyo's research has been generating an innovative and attractive pipeline, including anti-diabetes drugs. For further information about Sankyo, please consult http://www.sankyo.co.jp/english/