SAN DIEGO, CA - January 8, 2002-- Metabasis Therapeutics, Inc., a rapidly growing, clinical stage biopharmaceutical company, announced today that it has received a US patent covering its HepDirect™ Technology. The patent, US 6,312,662, broadly covers the technology and its medical uses as well as provides the company with claims to composition-of-matter, methods of manufacture and methods of use for key compounds. The HepDirect Technology is a proprietary platform technology discovered and developed by Metabasis that allows liver targeting of the biologically active form of a wide variety of drugs. Currently, two compounds in Metabasis' product pipeline utilize the HepDirect Technology. MB6866, the first clinical candidate generated from the technology, is a novel oral drug for Hepatitis B that was licensed to ICN Pharmaceuticals in October 2001. The second compound is a novel drug for treating primary liver cancer (hepatocellular carcinoma). Clinical testing of MB6866 is expected to begin next quarter and clinical testing of the liver cancer product is scheduled to begin in early 2003.

The HepDirect Technology entails the synthesis of a biologically inactive form of a drug, termed a HepDirect prodrug, which, following either oral or systemic administration, distributes throughout the body. Over time, a large proportion of the HepDirect prodrug circulates through the liver where it is selectively activated and converted to the biologically active form of the drug. In humans, the high liver specificity associated with HepDirect prodrugs is expected to significantly improve the safety and efficacy of drugs effective against liver-related diseases.

Dr. Paul Laikind, Chairman, CEO and President at Metabasis stated, "We are pleased to obtain this patent given its overall importance to our collaboration with ICN and our internal efforts to develop drugs based on the HepDirect Technology. The HepDirect Technology is allowing us to add at least two new products to our clinical stage pipeline over the next 18 months. These will be in addition to our new drug for diabetes, MB6322, which acts by a novel mechanism and is being developed by Sankyo Co., Ltd. MB6322 is expected to begin Phase 2 clinical testing this quarter."

Dr. Mark Erion, Executive Vice President of Research and Development, stated "This patent covers many of the critical elements of our technology. The patent is broad in scope with composition-of-matter claims to a large variety of drugs. In addition, the patent covers the manufacture of HepDirect prodrugs and their medical uses. We are using the HepDirect Technology in our HBV and liver cancer programs as well as in earlier stage research projects focused on the discovery of novel drugs for the treatment of hepatitis C, liver fibrosis and other liver-related disorders. Our research on the HepDirect Technology has been on-going for several years and comprises a vast number of in vitro and in vivo studies that not only led to this patent but should also enable Metabasis to further expand and strengthen its proprietary position in the area. We anticipate receiving additional patents in the US on our technology from both pending and future patent applications as well as obtaining strong patent coverage around the world. "

Metabasis also announced that it will make a corporate presentation at the JP Morgan H&Q 20th Annual Healthcare Conference on Tuesday, January 8, 2002, at 2:30 p.m. Pacific Time.

Metabasis Therapeutics, Inc. (http://www.mbasis.com) is a privately-held, biopharmaceutical company that develops proprietary products for the treatment of human disease with a current focus on diseases that involve the liver. The Company is a leader in the field of nucleoside/nucleotide metabolism and chemistry, and has proprietary expertise in liver biology and organ-specific drug delivery. The Company has developed the HepDirect™ prodrug technology that allows liver-specific delivery of new and existing drugs. The company has also discovered and developed a new class of drugs for treating diabetes that act to lower liver glucose production in diabetic patients. The first drug from this program is being developed in collaboration with Sankyo Co., Ltd. and is currently undergoing Phase 1 clinical testing. The Company occupies state-of-the-art research facilities in San Diego, California.