ISENTRESS(R) (raltegravir) from MSD, First Integrase Inhibitor, Approved by the European Union Commission

Merck Sharp & Dohme (MSD) announced today that ISENTRESS(R)
(raltegravir) has been granted a license from the European Union
Commission (Commission) by way of a decision for use in combination
with other antiretroviral medicinal products for the treatment of
HIV-1 infection in treatment-experienced adult patients with evidence
of HIV-1 replication despite ongoing antiretroviral therapy (ART). The
Commission´s decision is applicable to the 27 Member States of the
European Union (EU), including France, Germany, Italy, Spain and the
United Kingdom. Separate national licenses, based on the Commission´s
Decision, will also be issued in European Economic Area Member States
Iceland and Norway. Raltegravir is the first approved integrase
inhibitor, a new class of ART that works by targeting the integrase
enzyme, which is essential for HIV replication.

The Commission´s decision, reflecting the positive opinion of the
European Medicines Agency, was based on efficacy and safety data from
two double-blind, placebo-controlled trials of 24 weeks duration in
treatment-experienced patients. In these studies raltegravir, in
combination with optimised background therapy (OBT), significantly
reduced HIV RNA viral load (p less than 0.001), and significantly
increased CD4 cell counts (p less than 0.001). The efficacy and safety
of raltegravir have not been established in treatment-naive adult
patients or paediatric patients, although studies in these populations
are underway.

"Raltegravir is an important new advancement in the treatment of
HIV, because it is the first therapy in a new class of drugs that
attacks the virus in a completely different way from other available
medicines," said Ken Frazier, executive vice president and president,
Global Human Health, Merck & Co., Inc. "This approval marks another
milestone in MSD´s continued commitment to combating HIV and AIDS by
conducting research for breakthrough medicines, developing business
models that help our products reach as many people as possible, and
participating in partnerships to help build infrastructure and address
health and development challenges around the world."

Despite the availability of drugs to treat HIV and AIDS, the
pandemic continues. In the EU, nearly 250,000 cases of HIV have been
reported since 2002, according to the European Centre for the
Epidemiological Monitoring of HIV and AIDS. Additionally, resistance
to current HIV therapies in treatment-experienced patients has been
noted in numerous international studies, suggesting that resistance to
at least one class of antiretroviral agents may be as high as 76
percent. The World Health Organisation (WHO) has called resistance an
emerging public health concern and has partnered with the
International AIDS Society to develop the Global HIV Drug Resistance
Surveillance Network to track emerging resistance patterns in
developing and developed countries.

"Treatment-experienced HIV patients have limited options for
therapies that are well-tolerated and can reduce viral loads while
boosting CD4 counts," said Jurgen Rockstroh, professor of medicine and
head of the HIV Outpatient Clinic, University of Bonn, Germany. "The
approval of raltegravir in the EU represents a significant scientific
advancement, but more importantly, it addresses a much-needed
evolution in the treatment of HIV and AIDS."

Reduction in viral load and increase in CD4 cell counts

Raltegravir is being studied in two ongoing Phase III
multi-centre, double-blind, randomised, placebo-controlled studies
(BENCHMRK-1 and BENCHMRK-2) in 699 treatment-experienced adult
patients with documented resistance to at least one drug in each of
three classes (nucleoside reverse transcriptase inhibitors (NRTIs),
non-nucleoside reverse transcriptase inhibitors (NNRTIs) and protease
inhibitors (PIs)) of ARTs. Raltegravir 400 mg taken twice daily in
combination with OBT was significantly (p less than 0.001) more
effective at both reducing levels of HIV RNA and increasing CD4 cell
counts in these patients, when compared to a regimen of placebo plus
OBT. The efficacy responses were evaluated based upon the 699 patients
from the pooled studies who had completed 24 weeks of treatment or
discontinued earlier.

The studies showed that after 24 weeks of therapy, 75 percent of
patients (347 out of 462) receiving raltegravir in combination with
OBT achieved HIV RNA load reduction to below 400 copies/mL, compared
to 40 percent of patients (95 out of 237) receiving placebo plus OBT.
In addition, after 24 weeks of therapy, 63 percent of patients (289
out of 462) receiving raltegravir plus OBT achieved viral load
reduction to below 50 copies/mL, compared to 34 percent of patients
(80 out of 237) receiving placebo plus OBT. After 24 weeks of therapy,
increases in CD4 cell counts from baseline were 84 and 37 cells/mm(3)
for patients receiving raltegravir plus OBT and for those receiving
placebo plus OBT, respectively.

Raltegravir is a single 400 mg tablet taken twice daily without
regard to food. Raltegravir does not require boosting with ritonavir.
In Phase II and III clinical trials, the side effect profile was
comparable with placebo. The most common side effects are diarrhoea,
nausea, headache and pyrexia.

About raltegravir

Raltegravir is the first in a new class of antiretroviral agents
called integrase inhibitors. Raltegravir works by inhibiting the
insertion of the HIV DNA into human DNA by the 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 the other two enzymes critical to the HIV
replication process - protease and reverse transcriptase - but
raltegravir is the only drug approved that inhibits integrase.

Global filing status of raltegravir

Earlier this year, raltegravir received approval in the United
States, Mexico and Canada, and MSD is also moving forward with filings
in many countries around the world.

MSD history in HIV research

MSD is committed to developing innovative therapies that offer
advances in the treatment of infectious diseases - including HIV.
MSD´s efforts to develop investigational treatments for HIV have been
under way for more than 20 years and continue today. MSD began its HIV
integrase inhibitor research in 1993, and MSD was the first to
demonstrate inhibition of HIV integrase in vitro and in vivo.

Raltegravir is one part of MSD´s history in HIV research, which
includes the development of CRIXIVAN(R) (indinavir sulfate), a PI;
STOCRIN(R), a NNRTI; and research is currently underway on additional
treatment options.

Global prevalence of HIV and AIDS

An estimated 33 million people are living with HIV and AIDS
worldwide, and more than 2.5 million new infections occurred worldwide
in 2007.(i) AIDS is one of the top causes of infectious
disease-related mortality worldwide, responsible for more than two
million deaths last year alone.(ii)

About MSD

Merck & Co., Inc., Whitehouse Station, N.J., U.S.A. which operates
in many countries as MSD (Merck, Sharp & Dohme), is a global
research-driven pharmaceutical company dedicated to putting patients
first. Established in 1891, MSD 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 programmes that not only
donate MSD medicines but help deliver them to the people who need
them. MSD 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. MSD 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 MSD´s business, particularly those mentioned in the cautionary
statements in Item 1A of MSD´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.

(i) UNAIDS. 2007 AIDS Epidemic Update. Available at:
www.unaids.org/en/HIV_data/2007EpiUpdate/default.asp. Accessed on 28
November 2007.

(ii) World Health Organization. The global burden of disease: a
response to the need for comprehensive, consistent and comparable
global information on diseases and injuries. Available at:
www.who.int/mip/2003/other_documents/en/globalburdenofdisease.pdf.
Accessed on 26 November 2007.