AVI BioPharma Completes West Nile Virus Preclinical Development Program; Company Prepares for Human Clinical Studies of AVI 4020.

Business Editors/Health/Medical Writers

PORTLAND, Ore.--(BUSINESS WIRE)--April 24, 2003

AVI BioPharma, Inc. (Nasdaq:AVII), (Nasdaq:AVIIW), (Nasdaq:AVIIZ) today announced completion of its preclinical development program for its proprietary NEUGENE(R) antisense drug targeting the West Nile virus, AVI 4020.

AVI has begun formal discussions with the U.S. Food and Drug Administration (FDA) to begin human clinical trials evaluating AVI 4020. Following these discussions, AVI expects to submit an Investigational New Drug (IND) application and initiate a Phase I clinical trial later this year. To this end, AVI has begun manufacturing clinical supplies of AVI 4020 at the company's manufacturing facility in Corvallis, Ore.

AVI previously reported a successful field trial of its West Nile virus drug in the treatment of penguins infected with the virus in a Wisconsin zoo. Additional preclinical studies evaluated repeated exposures to AVI 4020 for 28 days. Measurements of blood levels and tissue distribution indicated no drug related toxicities and favorable drug distribution.

AVI has developed a unique research and development approach to rapidly respond to emerging infectious diseases. Using its NEUGENE antisense drugs, AVI can move from initial target identification to clinical programs quickly, particularly in response to single-stranded RNA viruses.

David H. Mason, Jr., M.D., senior vice president for Clinical Development and Regulatory Affairs at AVI, said, "We are pleased with the results of our preclinical program for AVI 4020, which adds to our experience with NEUGENE antisense drugs. NEUGENES have been evaluated in more than 200 patients in various indications, and continue to demonstrate a strong safety profile. We plan to move forward quickly to evaluate AVI 4020 in patients with West Nile virus, which represents a substantial unmet medical need. There are no effective treatments available for this very serious illness."

Serious West Nile virus infections are fatal in approximately 10 percent of affected patients, and may produce serious neurologic problems in many more patients. In 2002, approximately 4,000 cases of severe West Nile virus disease, and nearly 400 deaths, were recorded in the U.S. by the Centers for Disease Control (CDC). The virus infects the brain and surrounding structures and produces a variety of clinical effects, including meningitis, altered mental status, a paralysis similar to that seen with poliovirus infections, and, in the most severe cases, irreversible coma.

Patrick L. Iversen, Ph.D., senior vice president of Research and Development at AVI, said, "Our antiviral research program has produced antisense drugs active against West Nile virus, feline calicivirus, hepatitis C virus, and murine hepatitis virus, a coronavirus. These single-stranded RNA viruses are attractive targets for our NEUGENE antisense drugs. What we learn in our West Nile program will provide important information as we address other emerging viral diseases, including Severe Acute Respiratory Syndrome (SARS)."

About AVI BioPharma

AVI BioPharma develops therapeutic products for the treatment of life-threatening diseases using two technology platforms: NEUGENE antisense drugs and cancer immunotherapy. Its lead cancer agent, AVICINE(R), a therapeutic cancer vaccine, has completed three Phase II trials in colorectal and pancreatic cancer and is initiating a Phase III pivotal trial in pancreatic cancer, with a supporting study in colorectal cancer. The first application of its NEUGENE compounds, Resten-NG(TM), is designed to treat cancer, cardiovascular restenosis and other cell proliferation disorders by inhibiting the production of a cellular transcription factor, the oncogene c-myc. It is currently in Phase II trials for restenosis and in a Phase Ib trial for cancer. AVI has completed a Phase I NEUGENE antisense study that successfully down-regulated the liver enzyme cytochrome P450 and modified drug metabolism, and a Phase Ib trial in polycystic kidney disease. More information about AVI is available on the Company's Web site at http://www.avibio.com/.

"Safe Harbor" Statement under the Private Securities Litigation Reform Act of 1995: The statements that are not historical facts contained in this release are forward-looking statements that involve risks and uncertainties, including, but not limited to, the results of research and development efforts, the results of preclinical and clinical testing, the effect of regulation by the FDA and other agencies, the impact of competitive products, product development, commercialization and technological difficulties, and other risks detailed in the Company's Securities and Exchange Commission filings.