(Reuters) - Merck
& Co said once-daily use of its HIV drug Isentress was less
effective in a late-stage study than standard twice-daily dosing among
patients that had not previously been treated for the virus that causes
AIDS.
Based on the disappointing
initial results, the U.S. drugmaker said on Monday it was ending the
Phase III study, which could have paved the way for wider use among
previously untreated patients.
The
product is approved for use with other HIV medicines among previously
treated patients as well as those that have not yet undergone treatment.
It is the only approved HIV drug that works by blocking integrase -- an
enzyme that enables the virus to insert its genetic material into human
DNA.
"While a once-daily approval
would have been an upside event that could have resulted in more
first-line usage of Isentress over time, we do not see today's news as a
major negative for (Merck's) stock," J.P. Morgan analyst Chris Schott
said in a research note.
Merck
shares were down 1.4 percent at $34.36 in early afternoon trading on the
New York Stock Exchange, amid declines in the broad stock market.
Isentress is one of Merck's fastest-growing
medicines. Its sales leaped 41 percent in the third quarter to $278
million, putting it on track to become a $1 billion-a-year blockbuster.
Schott held to his forecast of annual
Isentress sales of $2 billion by 2015. But he said its later peak sales
will be less than they might have been, had the trial not failed.
One group in the 775-patient study received
800 milligrams of Isentress once daily, along with other HIV
treatments. Another group received the approved Isentress 400-milligram
dose given twice a day, also in combination with standard treatments.
After 48 weeks, HIV was driven to
undetectable levels in 83.2 percent of patients receiving the once-daily
regimen, which was deemed inferior to the 88.9 percent of patients who
received twice-daily tablets.