ViroPharma Completes Enrollment in Phase 2 Clinical Study of Maribavir in Bone Marrow Transplant Patients

Exton, Pennsylvania, UNITED STATES

EXTON, Pa., Nov. 28, 2005 (PRIMEZONE) -- ViroPharma Incorporated (Nasdaq:VPHM) today announced that it has completed enrollment in its Phase 2 clinical study for maribavir, an oral antiviral drug that inhibits cytomegalovirus (CMV), in allogeneic bone marrow (stem cell) transplant patients.

"CMV infection and associated disease is a significant cause of morbidity and mortality for patients undergoing hematopoietic stem cell and solid organ transplant," commented Colin Broom, M.D., ViroPharma's chief scientific officer. "Due to potential toxicities associated with current treatments, anti-CMV therapy is often initiated only when there is clear evidence of CMV infection; however, it would be preferable to administer anti-CMV therapy as prophylaxis to prevent CMV infection altogether. Our hope is that maribavir may offer transplant patients an effective option to prevent CMV infection with an improved safety profile compared to currently available therapies."

"We are delighted to have reached this milestone with maribavir, and continue to anticipate that we will have preliminary data from the Phase 2 trial available by the end of the first quarter of 2006. If the data are positive we expect to initiate Phase 3 testing mid-year 2006," continued Broom.

The Phase 2 clinical trial is a randomized, double blind, placebo-controlled, dose-ranging study at 13 transplant centers across the U.S. involving CMV-seropositive subjects who have undergone allogeneic stem cell transplantation. At least 36 subjects have been randomized 3:1 (ratio of maribavir to placebo) into each of three ascending dose groups for a total of at least 108 patients overall. The primary objective of this study is to evaluate the safety and tolerability of maribavir administered orally for up to 12 weeks. The secondary objectives are to evaluate the prophylactic activity of maribavir in preventing CMV reactivation in CMV seropositive recipients of allogeneic stem cell transplants, to evaluate the pharmacokinetics of maribavir in this subject population, and to select a dose or doses of maribavir to be used in the Phase 3 program.

Maribavir is a novel antiviral compound in development by ViroPharma. It is a potent and selective, orally bioavailable antiviral drug with a unique mechanism of action against cytomegalovirus and a favorable early clinical safety profile. It is a potent member of a new class of drugs called benzimidazole ribosides. Unlike currently available anti-CMV agents that inhibit CMV DNA polymerase, maribavir inhibits viral DNA assembly and inhibits egress of viral capsids from the nucleus of infected cells. Maribavir is active in vitro against strains of CMV that are resistant to commonly used anti-CMV drugs. ViroPharma licensed maribavir from GlaxoSmithKline in August 2003.

CMV is a member of the herpes virus group, which includes the viruses that cause chicken pox, mononucleosis, herpes labialis (cold sores), and herpes genitalis (genital herpes). Like other herpesviruses, CMV has the ability to remain dormant in the body for long periods of time. Human CMV infection rates average between 50% and 85% of adults in the U.S. by 40 years of age, but in healthy adults causes little to no apparent illness. However, in immunocompromised individuals, CMV can lead to serious disease or death. Patients who are immunosuppressed following hematopoietic stem cell (bone marrow) or solid organ transplantation are at high risk of CMV infection. In these patients, CMV can lead to severe conditions such as pneumonitis or hepatitis, or to complications such as acute or chronic rejection of a transplanted organ. While currently available systemic anti-CMV agents are effective against the virus, their use is limited by toxicities, most notably bone marrow suppression and renal impairment.

About ViroPharma Incorporated

ViroPharma Incorporated is a biopharmaceutical company dedicated to the development and commercialization of products that address serious diseases treated by physician specialists and in hospital settings. ViroPharma commercializes Vancocin(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 may contain forward-looking statements that involve a number of risks and uncertainties, including those relating to our hope that maribavir may offer transplant patients a better tolerated, efficacious treatment option, our expected timeframe for the availability of maribavir Phase 2 data, and our estimated date for initiating Phase 3 studies with maribavir. Our actual results could differ materially from those results expressed in, or implied by, these forward-looking statements. The development and commercialization of pharmaceutical products is subject to risks and uncertainties. There can be no assurance that that our Phase 2 studies will yield positive results, that we will initiate Phase 3 studies, that the program will meet the timelines described in this press release, or that maribavir will ever be approved by the FDA. These factors, and other factors, including, but not limited to those described in ViroPharma's quarterly report on Form 10-Q for the period ended September 30, 2005, 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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