Merck & Co., Inc. announced today that the U.S. Food and Drug Administration (FDA) has accepted the New Drug Application (NDA) for ISENTRESS™ (raltegravir, previously known as MK-0518). Data in the NDA support the proposed use of ISENTRESS in combination with other antiretroviral agents for the treatment of HIV-1 infection in treatment-experienced patients with evidence of HIV-1 replication despite ongoing antiretroviral therapy (ART).

The FDA granted ISENTRESS priority review status, a designation for investigational products that address unmet medical needs. Under the priority review designation, the FDA is expected to review and act on the NDA for ISENTRESS within six months of submission. Merck anticipates FDA action by mid-October and as planned is also moving forward with regulatory filings in countries outside of the United States.

If approved, ISENTRESS would be the first in a new class of antiretroviral agents called integrase inhibitors that inhibit the insertion of HIV DNA into human DNA. Inhibiting integrase from performing this essential function blocks the ability of the virus to replicate and infect new cells. There are drugs in use that inhibit two other enzymes critical to the HIV replication process – protease and reverse transcriptase – but currently no approved drugs inhibit integrase.

"ISENTRESS underscores Merck's commitment to developing and marketing medications that address unmet medical needs," said Peter S. Kim, Ph.D., president, Merck Research Laboratories. "ISENTRESS is a novel approach for treatment-experienced patients with HIV, a population in need of additional options."

The application included data from Phase II and Phase III clinical trials in which ISENTRESS was used in combination with optimized background therapy (OBT) in treatment-experienced HIV patients failing ARTs who were infected with virus resistant to at least one drug in each of the three available classes of oral ARTs. The formulation of ISENTRESS under review is a single 400mg tablet dosed twice daily without regard to food and which does not require boosting with ritonavir. Merck also is conducting ongoing clinical trials of ISENTRESS in the treatment-naïve (previously untreated) HIV population.

Expanded access program
ISENTRESS is currently available, at no charge, to qualified patients through an expanded access clinical research program, EARMRK. The global program provides early access to ISENTRESS for patients who are resistant to existing classes of antiretroviral medications and who require an HIV treatment regimen containing a medication to which they may not be resistant.

Prevalence of HIV/AIDS
Despite the availability of drugs to treat HIV/AIDS, the global epidemic continues. Current estimates indicate that approximately 40 million people are infected worldwide, and more than 4 million new infections occurred worldwide in 2006. AIDS is one of the top causes of infectious disease-related mortality worldwide, responsible for approximately 3 million deaths last year.i

Merck HIV research
Merck's efforts to develop investigational treatments and a vaccine against HIV/AIDS have been under way for almost 20 years and continue today. Merck began its HIV integrase inhibitor research in 1993, and Merck was the first to demonstrate inhibition of HIV integrase in vitro and in vivo.

About Merck
Merck & Co., Inc. is a global research-driven pharmaceutical company dedicated to putting patients first. Established in 1891, Merck currently discovers, develops, manufactures and markets vaccines and medicines to address unmet medical needs. The Company devotes extensive efforts to increase access to medicines through far-reaching programs that not only donate Merck medicines but help deliver them to the people who need them. Merck also publishes unbiased health information as a not-for-profit service. For more information, visit www.merck.com.