Pharmasset’s experimental hepatitis C therapies may pose a challenge to treatments from Vertex Pharmaceuticals, based on trial results to be released in late March, BMO Capital Markets Corp. analysts said, according to a Bloomberg report.

Two drugs from Pharmasset showed “impressive” figures as stand-alone medications or combination therapies, while results from a two-drug combination from Vertex did not justify further patient studies, the analysts, led by Jason Zhang in Montreal, wrote in a research report to investors, citing abstracts of the trials.

The Vertex trial combined its drug telaprevir, due for U.S. regulatory review on May 23, with experimental drug VX-222, Zhang wrote. The Pharmasset trials combined two experimental therapies, PSI-7977 and PSI-938, with standard therapies or with each other. Zhang lowered his recommendation on Vertex’s stock from “outperform” to “market perform,” saying investors already expect telaprevir to be approved.

“The hepatitis C treatment landscape subsequent to the initial phase of telaprevir dominance is tilting away from Vertex to companies such as Pharmasset that have potent combinations,” Zhang wrote.