NEW YORK -- Vertex Pharmaceuticals Inc. said a study shows its hepatitis C drug telaprevir can be dosed twice per day instead of three times, and Vertex shares shot to their highest price in two years.

Results from the small midstage clinical trial showed Vertex's pill, telaprevir, was about as effective at eliminating the hepatitis C virus if it was given twice a day as it was when given three times a day. In most of Vertex's studies, the drug has been dosed three times a day, and more convenient dosing could help sales if telaprevir is approved.

In afternoon trading, shares of the Cambridge, Mass., company climbed $2.95, or 8.8 percent, to $36.51. Earlier they rose to $38.68, which was the stock's highest price since October 2007.

In the study, 161 patients were given telaprevir every eight or 12 hours. They also took standard hepatitis C treatments: infusions of an interferon drug, which is given once a week, and a twice-per-day antiviral pill called ribavirin. Vertex said more than 80 percent of patients in each group experienced a sustained viral response, meaning their levels of the hepatitis C virus were so low they became undetectable. That response, called an SVR, is the goal of hepatitis C treatment.

Dosing with telaprevir lasted for 12 weeks, and treatment with the other drugs continued for another 12 weeks.

BMO Capital Markets analyst Jason Zhang said that several experimental drugs that could compete with telaprevir are also intended to be given twice a day.

"What investors will particularly like is that the SVRs are almost the same in the four groups, suggesting that telaprevir would most likely to be used as a twice-daily drug," said Jason Zhang.

Results from the trial, called C208, were presented on Saturday at a meeting of the American Association for the Study of Liver Diseases. None of the subjects in the trial had received any previous treatment.

Vertex is almost done with late-stage clinical trials of telaprevir and will file for marketing approval in late 2010. The company said it had not tested telaprevir twice a day before, but it will discuss the requirements for marketing twice daily telaprevir with U.S. and European Union regulators.

Vertex is planning to make a full presentation of data from the European study Tuesday morning in Boston. More than 6.8 million Vertex shares changed hands by 2 p.m. Monday. On a typical day, about 1.7 million shares are traded.