FDA Advisory Committee Unanimously Recommends Accelerated Approval of ISENTRESS(TM) (raltegravir), Merck's Investigational Oral Integrase Inhibitor, for Treatment of HIV

Merck & Co., Inc. announced today that the Antiviral Drugs
Advisory Committee of the U.S. Food and Drug Administration (FDA)
voted unanimously to recommend accelerated FDA approval of
ISENTRESS(TM) (raltegravir) in combination with other antiretroviral
therapy (ART) for the treatment of HIV infection in
treatment-experienced patients with ongoing viral replication despite
existing therapy.

If approved, ISENTRESS would be the first in a new class of
antiretroviral agents called integrase inhibitors available for the
treatment of HIV. The FDA is not bound by the committee's
recommendation but takes its advice into consideration when reviewing
investigational medicines.

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 New Drug Application for ISENTRESS within six months of
submission. Merck anticipates FDA action by mid-October.

"ISENTRESS is an important example of our ongoing commitment to
HIV research," said Peter S. Kim, Ph.D., president, Merck Research
Laboratories. "Despite the availability of various treatment options,
the HIV epidemic continues, so there remains a need for new
therapeutic approaches. This positive recommendation signals an
important step forward for the treatment of patients living with HIV."

In addition to the FDA regulatory application, Merck is also
moving forward with regulatory filings in countries outside of the
United States.

The advisory committee's recommendation was based on review of
efficacy and safety results from studies with ISENTRESS used in
combination with optimized background therapy in treatment-experienced
HIV-infected patients who had failed antiretroviral therapies, and who
had HIV resistant to at least one drug in each of three classes of
oral ARTs.

About ISENTRESS

ISENTRESS works to inhibit the insertion of HIV DNA into human DNA
by the viral integrase enzyme. 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 that inhibit
integrase.

Prevalence of HIV/AIDS

In 2003, over one million Americans were living with HIV and it is
estimated that approximately 40,000 new cases of HIV/AIDS are
diagnosed each year in the U.S. (i) Worldwide, an estimated 40 million
people are infected with HIV/AIDS, and more than four million new
infections occurred in 2006.(ii) AIDS is one of the top causes of
infectious disease-related mortality worldwide, responsible for nearly
three million deaths last year alone.(iii)

Merck HIV research

Merck's efforts to develop investigational treatments and a
vaccine against HIV/AIDS have been under way for more than 20 years
and continues 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.

Forward-looking statement

This press release contains "forward-looking statements" as that
term is defined in the Private Securities Litigation Reform Act of
1995. These statements are based on management's current expectations
and involve risks and uncertainties, which may cause results to differ
materially from those set forth in the statements. The forward-looking
statements may include statements regarding product development,
product potential or financial performance. No forward-looking
statement can be guaranteed, and actual results may differ materially
from those projected. Merck undertakes no obligation to publicly
update any forward-looking statement, whether as a result of new
information, future events, or otherwise. Forward-looking statements
in this press release should be evaluated together with the many
uncertainties that affect Merck's business, particularly those
mentioned in the risk factors and cautionary statements in Item 1A of
Merck's Form 10-K for the year ended Dec. 31, 2006, and in its
periodic reports on Form 10-Q and Form 8-K, which the company
incorporates by reference.

ISENTRESS(TM) is a trademark of Merck & Co., Inc.

(i) CDC HIV/AIDS Fact Sheet "A Glance at the HIV/AIDS Epidemic,"
June 2007

(ii) UNAIDS, 2006 Report on the Global AIDS Epidemic

(iii) UNAIDS and WHO. AIDS Epidemic Update. December 2006.