ViroPharma Announces Advancement of HCV-796 Into Phase 1B Clinical Testing In Hepatitis C Patients

Exton, Pennsylvania, UNITED STATES

EXTON, Pa., May 24, 2005 (PRIMEZONE) -- ViroPharma Incorporated (Nasdaq:VPHM) today announced the commencement of a Phase 1b proof of concept clinical study in hepatitis C positive patients with HCV-796, a novel antiviral compound that the company is co-developing with Wyeth Pharmaceuticals, a division of Wyeth (NYSE:WYE). HCV-796 is a potent orally dosed compound that has the potential to interfere with the replication of hepatitis C virus (HCV). Preclinical studies have shown that HCV-796 is the most potent of all anti-HCV compounds developed to date between the two companies.

"Throughout the history of our partnership, ViroPharma and Wyeth Pharmaceuticals together have identified a series of compounds targeting the hepatitis C virus. HCV-796 is by far the most potent, demonstrating nanomolar potency in replicon containing cells and significant activity in a mouse model of HCV infection," commented Colin Broom, M.D., ViroPharma's chief scientific officer. "In our recently completed single dose study, escalating doses of HCV-796 were well tolerated with favorable pharmacokinetics, consistent with our experience of a predecessor molecule. With HCV-796, we also have the major advantage of at least a 22-fold increase in potency, based on replicon data. We are very encouraged as we expeditiously move forward with this compound, and expect to have data from this trial in the fourth quarter of 2005."

Preclinical Data

To date, HCV-796 has demonstrated potent efficacy in inhibiting viral replication in cell-based assay systems and in an animal model for hepatitis C. In these studies, HCV-796 antiviral activity was highly selective and significantly reduced HCV RNA levels in an in vitro replicon assay, a cell-based system in which the antiviral activity of a compound can be tested against HCV RNA replicating in a human cell line, with an EC50 (the effective concentration at which viral replication is reduced by 50 percent) of 5nM against genotype 1a and 9nM against genotype 1b. This represents a 128-fold and 22-fold increase in potency, respectively, compared to data generated for the predecessor molecule HCV-086.

In addition, HCV-796 has shown significant antiviral activity as a single agent in chimeric mice that support HCV infection, and appears to be additive with interferon alpha as a combined treatment.

Phase 1b Study Design

This clinical trial is a randomized, double blind, multiple ascending dose, placebo controlled study at a leading clinical research facility in the United States involving 96 patients naive to treatment with chronic HCV infection. In the study, patients will be given multiple ascending oral doses of HCV-796 for fourteen days. The study will assess the antiviral activity, safety, and pharmacokinetic profile of the drug compared to placebo.

ViroPharma and Wyeth have completed a single dose, placebo controlled, dose escalation Phase 1 trial with HCV-796, to assess the safety, tolerability and pharmacokinetics of the compound administered orally to healthy volunteers. Preliminary data from this single dose trial indicate that HCV-796 was well tolerated at all doses tested, with a favorable pharmacokinetic profile.

About Hepatitis C

Hepatitis C is a blood-borne virus recognized as a major cause of chronic hepatitis worldwide. The World Health Organization estimates that 170 million persons worldwide are chronically infected with HCV, and three to four million persons are newly infected globally each year. According to the U.S. Centers for Disease Control and Prevention (CDC), about four million people in the U.S., or 1.8 percent of the population, are infected with HCV.

About ViroPharma Incorporated

ViroPharma Incorporated is committed to the development and commercialization of products that address serious diseases treated by physician specialists and in hospital settings. ViroPharma commercializes Vancocin(R) Pulvules(R), approved for oral administration for treatment of antibiotic-associated pseudomembranous colitis caused by Clostridium difficile and enterocolitis caused by Staphylococcus aureus, including methicillin-resistant strains (for prescribing information, please download the package insert at ViroPharma currently focuses its drug development activities in viral diseases including cytomegalovirus (CMV) and hepatitis C (HCV). For more information on ViroPharma, visit the company's website at

Certain statements in this press release contain forward-looking statements that involve a number of risks and uncertainties, including those relating to the company's anticipated schedule relating to its HCV clinical development program as well as its ability to find an effective small molecule antiviral treatment for HCV disease. Our actual results could differ materially from those results expressed in, or implied by, these forward-looking statements. Conducting clinical trials for investigational pharmaceutical products is subject to risks and uncertainties. Also, there is no validated animal or other preclinical model for HCV, and thus preclinical results for HCV-796, including animal efficacy data, are not necessarily predictive of safety or efficacy in the humans. There can be no assurance that ViroPharma's HCV studies can be conducted within the timeframe that the company expects, that such studies will yield positive results, or that ViroPharma will be successful in gaining regulatory approval of any of its HCV product candidates. These factors, and other factors, including, but not limited to those described in ViroPharma's quarterly report on Form 10-K for the year ended December 31, 2004 filed with the Securities and Exchange Commission, could cause future results to differ materially from the expectations expressed in this press release. The forward-looking statements contained in this press release may become outdated over time. ViroPharma does not assume any responsibility for updating any forward-looking statements.


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