Federal regulators have put a “partial clinical hold” on a mid-stage study of an experimental oral drug developed by Vertex Pharmaceuticals Inc. to treat hepatitis C.
The move will prevent the Cambridge company from giving clinical trial patients 200 milligram doses of the pill, which would be used in combination with other oral therapies to treat the virus.
Vertex already has an oral hepatitis C treatment on the market, but it is used in combination with an injectable drug.
A Vertex spokesman, Zach Barber, said that the Food and Drug Administration ordered the hold after three patients in a European trial showed elevated liver enzymes — a potential marker of liver damage — when taking 400 milligram doses.
The US trial was designed to use only 100 milligram and 200 milligram dosing levels, he said. Vertex will continue with its 100 milligram dosing.
“The FDA has requested data from us, and we’ll be providing that data on an ongoing basis” to gauge the effect of the drug candidate on patients, Barber said. “Hepatitis C remains an important part of our business and with multiple ongoing studies of [the experimental pill], our strategy is unchanged.”