Washington Editor

ViroPharma Inc. began the first of two Phase III studies of maribavir in transplant patients.

This initial trial will evaluate the prophylactic use of maribavir in stem cell transplant patients to prevent cytomegalovirus (CMV) disease in them. The product's pharmacokinetics also will be evaluated in the randomized, double-blinded, placebo-controlled study, which will enroll about 500 patients who have undergone allogeneic stem cell transplantation.

The primary endpoint will measure the incidence of CMV disease within 180 days after transplant, which is predicted to be about 10 percent in the placebo (current standard of care) arm. Secondary endpoints include the incidence of initiation of preemptive anti-CMV therapy, incidence of graft-vs.-host disease, mortality and CMV disease-free survival.

Recruitment is planned to last 18 months. The Exton, Pa.-based company's treatment goal is to position maribavir as an efficacious and specific antiviral therapy for transplant patients, with a more favorable side-effect profile than currently available therapies.

In the study, which will take place across the U.S., Canada and several European countries, maribavir will be administered orally for up to 12 weeks. Phase II data showed the drug to be well tolerated and demonstrated its antiviral activity in preventing CMV infections after transplant. Of note, no maribavir-treated patients developed CMV disease, compared to an incidence of 11 percent of placebo patients.

The antiviral, which belongs to a new class of drugs called benzimidazole ribosides, inhibits viral DNA assembly and inhibits egress of viral capsids from the nucleus of infected cells.

Later this year, ViroPharma plans to begin a Phase III trial in solid organ transplant patients. The company estimated that 46,000 patients undergo stem cell or solid organ transplants in the U.S. each year.

On Friday, its stock (NASDAQ:VPHM) fell 24 cents to close at $12.17.