ViroPharma Incorporated has announced that the U.S. Food and Drug Administration (FDA) has granted fast track designation for maribavir, an oral antiviral drug candidate for the prevention of cytomegalovirus (CMV) infection in allogeneic bone marrow (stem cell) and solid organ transplant patients.

ViroPharma completed enrollment in a Phase 2 study of maribavir in recipients of bone marrow (stem cell) transplant in November 2005, and expects to release the preliminary data from the trial by the end of the first quarter of 2006.

“There is an unmet medical need for improved treatments for the prevention of cytomegalovirus infection and disease in transplant patients due to the limitations of current therapies, which include potential bone marrow and renal toxicities,” commented Colin Broom, M.D., ViroPharma’s chief scientific officer.

“Fast track designation is an important step in accelerating our efforts to provide a much-needed therapeutic option for these patients. We look forward to working closely with the FDA throughout the process.”

An important feature of fast track designation is that it emphasizes the critical nature of close, early communication between the FDA and the sponsor company with the goal of improving the efficiency of product development. Under the FDA Modernization Act of 1997, fast track designation may potentially expedite the review and accelerate approval of a drug that is intended for the treatment of a serious life-threatening condition and demonstrates the potential to address an unmet medical need for such a condition.

Maribavir 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.

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.

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