Reuters NewMedia - February 9, 2012
(Reuters) - Merck & Co's recently approved Victrelis treatment
for hepatitis C considerably lessens the effectiveness of some
widely used medicines against the virus that causes AIDS, Merck
and U.S. regulators said in separate reports.
"These drug interactions may be clinically significant for
patients infected with both chronic hepatitis C virus and HIV by
potentially reducing the effectiveness of these medicines when
co-administered," Merck said in a February 6 letter to healthcare
Victrelis, approved last May, attacks the hepatitis C virus that
over decades can lead to cirrhosis and liver failure. A
significant percentage of hepatitis patients are also infected
with the human immunodeficiency virus, or HIV, which weakens the
immune system and is fatal without treatment.
The drug interactions were seen in a study among healthy
volunteers who took Victrelis and the widely used HIV treatment
Norvir in combination with one of three other anti-HIV pills:
Reyataz (atazanavir), Prezista (darunavir) and Kaletra
(lopinavir/ritonavir). All of the HIV drugs work by blocking
protease, an enzyme the virus requires to replicate.
Victrelis reduced concentrations in the blood of Reyataz,
Prezista and Kaletra by an average 49 percent, 59 percent and 43
Further, levels of Victrelis itself were reduced by 45 percent
among volunteers who took it with Kaletra, and 32 percent among
those who took it with a combination of Norvir and Prezista.
ISI Group analyst Mark Schoenebaum said 10 percent to 15 percent
of patients with hepatitis C are co-infected with HIV, and the
findings could crimp Victrelis sales by as much as 25 percent.
But he said the setback would have little impact on Merck's
earnings this year or in 2013.
The reduced prospects for Victrelis come even as its sales are
being dwarfed by Vertex Pharmaceuticals Inc's Incivek, a rival
protease inhibitor that was also approved last May.
The U.S. Food and Drug Administration, in an announcement of the
findings that appeared on the agency's website on Wednesday, said
patients should not stop taking any of their medicines without
talking to healthcare professionals.
Drug interactions had previously been found between Victrelis and
another HIV treatment called Sustiva (efavirenz). Sustiva belongs
to a family of HIV drugs called non-nucleoside reverse
transcriptase inhibitors (NNRTIs).
Merck said it was conducting drug-interaction studies of
Victrelis with other HIV drugs. They include Intelence
(etravirine), which is also a NNRTI, and Isentress (raltegravir),
which belongs to a class of drugs called HIV integrase
Merck shares slid 14 cents to $38.28 in afternoon trading on the
New York Stock Exchange.
(Reporting By Ransdell Pierson; editing by John Wallace and