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May 23, 2013 4:00 pm ET

Merck (NYSE: MRK), known as MSD outside the United States and Canada,
today provided an update on the clinical program for preladenant,
Merck’s investigational adenosine A2_A receptor antagonist for
the treatment of Parkinson’s disease (PD). An initial review of data
from three separate Phase III trials did not provide evidence of
efficacy for preladenant compared with placebo.

Based on these results, Merck is taking steps to discontinue the
extension phases of these studies and no longer plans to pursue
regulatory filings for preladenant. The decision to discontinue these
studies is not based on any safety finding. The results of these studies
will be presented at an upcoming scientific meeting and will be
submitted for publication in a peer-reviewed journal.

“While these results are disappointing, this program is an important
example of Merck’s continued commitment to pursue promising science with
the goal of bringing forward medicines that address important unmet
medical needs,” said David Michelson, M.D., vice president, clinical
research, Neuroscience and Ophthalmology at Merck Research Laboratories.
“Parkinson’s disease is very complex, making it difficult to treat
patients and develop novel therapeutic approaches. We are committed to
neuroscience research and will be conducting further analyses of the
data to inform the scientific community’s efforts in finding new
approaches to treat this debilitating disease. We thank the
investigators and importantly the Parkinson’s patients who participated
in the preladenant clinical program.”

The Phase III clinical program for preladenant included three
randomized, controlled clinical trials to evaluate safety and efficacy.
Two of these studies assessed preladenant when added to levodopa therapy
in patients with moderate-to-severe PD, and one assessed preladenant as
monotherapy in early PD. More information about the preladenant Phase
III clinical trials is available on www.clinicaltrials.gov.

About Merck

Today’s Merck is a global healthcare leader working to help the world be
well. Merck is known as MSD outside the United States and Canada.
Through our prescription medicines, vaccines, biologic therapies, and
consumer care and animal health products, we work with customers and
operate in more than 140 countries to deliver innovative health
solutions. We also demonstrate our commitment to increasing access to
healthcare through far-reaching policies, programs and partnerships. For
more information, visit www.merck.com
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Merck forward-Looking Statement

This news release includes “forward-looking statements” within the
meaning of the safe harbor provisions of the United States Private
Securities Litigation Reform Act of 1995. These statements are based
upon the current beliefs and expectations of Merck’s management and are
subject to significant risks and uncertainties. There can be no
guarantees with respect to pipeline products that the products will
receive the necessary regulatory approvals or that they will prove to be
commercially successful. If underlying assumptions prove inaccurate or
risks or uncertainties materialize, actual results may differ materially
from those set forth in the forward-looking statements.

Risks and uncertainties include but are not limited to, general industry
conditions and competition; general economic factors, including interest
rate and currency exchange rate fluctuations; the impact of
pharmaceutical industry regulation and health care legislation in the
United States and internationally; global trends toward health care cost
containment; technological advances, new products and patents attained
by competitors; challenges inherent in new product development,
including obtaining regulatory approval; Merck’s ability to accurately
predict future market conditions; manufacturing difficulties or delays;
financial instability of international economies and sovereign risk;
dependence on the effectiveness of Merck’s patents and other protections
for innovative products; and the exposure to litigation, including
patent litigation, and/or regulatory actions.

Merck undertakes no obligation to publicly update any forward-looking
statement, whether as a result of new information, future events or
otherwise. Additional factors that could cause results to differ
materially from those described in the forward-looking statements can be
found in Merck’s 2012 Annual Report on Form 10-K and the company’s other
filings with the Securities and Exchange Commission (SEC) available at
the SEC’s Internet site (www.sec.gov).

Merck
Media Contacts:
Pam Eisele, 908-423-5042
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