'Isentress'(R) (raltegravir), Merck Sharp & Dohme Limited's (MSD) treatment for HIV infection, has received a positive opinion from the Committee for Medicinal Products for Human Use (CHMP) of the European Medicines Evaluation Agency (EMEA) in Europe. The CHMP opinion for a conditional marketing authorisation recommends that raltegravir is used in combination with other antiretroviral medicinal products for the treatment of human immunodeficiency virus (HIV-1) infection in treatment-experienced adult patients with evidence of HIV-1 replication despite ongoing antiretroviral therapy. A conditional marketing authorisation is granted to a medicinal product that fulfils an unmet medical need when the benefit to public health of immediate availability outweighs the risk inherent in the fact that additional data are still required. The marketing authorisation holder is likely to provide comprehensive clinical data at a later stage. The CHMP, comprised of regulators from all European Union countries, gave the positive opinion following a review of data supporting the efficacy, safety and tolerability profile of raltegravir. Following the conclusion of the CHMP's review, its opinion will be transmitted to the European Commission (EC). If the EC adopts the opinion, raltegravir will be the first integrase inhibitor approved for use in the treatment of HIV-1 infection.

The CHMP decision will apply to the 27 countries that are members of the European Union, including the United Kingdom, Germany, France, Italy and Spain. After undergoing fast-track review by the Food and Drug Administration, raltegravir was approved in the United States on 12 October 2007. We anticipate a decision from the CHMP on the approval of the product in Q1 2008.

Chris Round, Managing Director of MSD, commented, "The advent of raltegravir, used in combination with other antiretroviral medicines, represents a significant milestone in the treatment of HIV infection. Up until now, highly treatment-experienced adult HIV patients, whose infection is not well controlled by their existing antiretroviral drugs, have had very few treatment options. With this, the first integrase inhibitor, a new treatment approach for this patient population is now within our sights."

About raltegravir Raltegravir, to be used in combination with other antiretroviral medicines, offers a new therapeutic option in the management of HIV and AIDS. Up until now, there have been drugs in use that inhibit two other enzymes that play a key role in propagating HIV infection - protease and reverse transcriptase - but there have not, to date, been any approved drugs that inhibit integrase.

Raltegravir, previously referred to as MK-0518, is the first in a new class of antiretroviral agents called integrase inhibitors. Integrase is an enzyme only found in viruses. There is no corresponding enzyme in humans. Integrase is used by HIV to insert its newly made genetic material (DNA) into the host cell's DNA. Inhibiting integrase from performing this function blocks the ability of the virus to replicate and infect new cells.

Tolerability profile of raltegravir

Results from pooled safety analyses from three separate studies in treatment-experienced patients taking 400 mg of raltegravir dosed twice daily plus OBT* or placebo plus OBT showed that after 24 weeks of therapy the rates of discontinuation of therapy due to adverse experiences were 2.0 percent in patients receiving raltegravir plus OBT and 1.4 percent in patients receiving placebo plus OBT.1 In addition, drugrelated clinical adverse events of moderate to severe intensity occurring in 2 percent or more patients were diarrhoea (3.7 percent vs. 3.5 percent), nausea (2.2 percent vs. 3.2 percent) and headache (2.2 percent vs. 1.4 percent) for raltegravir plus OBT and placebo plus OBT, respectively.2

Prevalence of HIV

Prevalence of HIV in the UK has shown a marked increase since the early 1980s.3 In 2005, there were an estimated 63,500 people living with HIV in the UK.3

About Merck Sharp & Dohme Limited (MSD)

Merck Sharp & Dohme Limited (MSD) is the UK subsidiary of Merck & Co., Inc., of Whitehouse Station, New Jersey, USA, a leading research-based pharmaceutical company that discovers, develops, manufactures and markets a wide range of innovative pharmaceutical products to improve human health. Merck & Co., Inc. has over twenty years of history in HIV research, which includes the protease inhibitor 'Crixivan' (indinavir), the non-nucleoside reverse transcriptase inhibitor efavirenz, and we continue the search for a vaccine for HIV.

The company began its HIV integrase inhibitor research in the early 1990s, and was the first to demonstrate integrase strand transfer inhibition, and to define the mechanism of action. Merck & Co., Inc. was also the first to demonstrate HIV integrase inhibitor's antiviral inhibition in vitro and in vivo. * OBT: Optimised background therapy is a regime of active antiretroviral drugs tailored to individual patients, chosen by their physicians as most likely to be of benefit.

This press release contains "forward-looking statements" about product development, product potential or about financial performance based on current expectations of the management of Merck & Co., Inc. No forward-looking statement can be guaranteed, and results may differ materially from those projected. Merck & Co., Inc. undertakes no obligation to publicly update any forward-looking statement, whether as a result of new information, future events, or otherwise.

Note:

'Isentress'® [pronounced i-sen-triss] is a Registered Trademark of Merck & Co., Inc., Whitehouse Station, New Jersey, USA.

References

1 Summary of Product Characteristics
2 Data on file
3 Health Protection Agency "A Complex Picture" HIV and other Sexually Transmitted Infections in the United Kingdom: 2006.

Merck Sharp & Dohme Limited