Achillion Pharmaceuticals announced receipt of regulatory clearance and the commencement of a Phase 2 clinical study with Company's lead product candidate, ACH-126,443 (Beta-L-Fd4C), in patients with HIV/AIDS. The study is being conducted under Achillion's second Investigational New Drug Application (IND) cleared by the US Food and Drug Administration (FDA), allowing the Company to conduct clinical development in a second therapeutic indication.

"This second IND in two years expands our clinical development activities from chronic hepatitis B infection into the therapeutic area of HIV. It also reflects our commitment to bring new medicines rapidly onto the market to treat patients having drug resistant forms of infectious diseases," said William G. Rice, Achillion's Chief Executive Officer.

This study (study 443-006) will assess suppression of viral replication by ACH-126,443 in patients with HIV infection. The patients to be enrolled in this double-blind study will maintain their combination therapy and will be randomized to continue lamivudine or to replace it with ACH-126,443, administered once a day. The 443-006 study will be conducted in multiple centers across North America.

"The pre-clinical data on ACH-126,443 indicate potency against many HIV strains, particularly those that are resistant to the most commonly prescribed anti-HIV drugs," commented Lisa M. Dunkle, MD, Senior Vice President of Drug Development for Achillion. "The need for new drugs to combat drug resistant HIV remains high, due to the ability of the virus to mutate easily."

ACH-126,443 is an L-nucleoside antiviral agent administered orally once daily that has demonstrated in vitro activity against HIV, including lamivudine-resistant and multi-drug resistant strains. Over 40 million people worldwide were estimated by the World Health Organization to be living with HIV/AIDS at the end of 2001, including over 900,000 individuals in the US. The Centers for Disease Control estimates that over one-half of US HIV/AIDS patients are infected with strains that are resistant to at least one class of existing drugs, and that up to 16 percent of new HIV infections are due to drug-resistant strains.

Achillion has demonstrated that ACH-126,443 also effectively inhibits replication of hepatitis B virus (HBV) in human clinical trials, and a series of clinical studies are underway to evaluate the efficacy of the agent in patients with wild-type and lamivudine-resistant strains of HBV. Chronic HBV infection is the world's ninth leading cause of death, according to the World Health Organization, and affects more than 350 million individuals worldwide.