The US Food and Drug Administration has approved Merck's new HIV drug Isentress (raltegravir) tablets to be used only along other antiretroviral agents for HIV-1 infection for adult patients who have evidence of viral replication and who have developed resistance to multiple antiretroviral agents.

Merck's new HIV drug Isentress (active substance: raltegravir) belongs to the antiretroviral integrase inhibitor class. Integrase is an enzyme that is used by the HIV virus to integrate its genetic material into human cells, and raltegravir interferes with this process by inhibiting the enzyme.

Raltegravir's chemical formula is C₂₀H₂₁FN₆O₅. Recently, an advisory panel for the U.S. Food and Drug Administration has recommended rapid government approval from the U.S. Food and Drug Administration because of its proven effectiveness in Phase III trials.

However, further trials will be needed before considering its approval for new HIV patients and children. Merck said it worked with the HIV community on the drug's pricing, and has priced Isentress at $27 per day, or less than $10,000 a year.

Thus, Isentress (raltegravir) is the only approved drug which prohibits the integrase enzyme, while other existing drugs inhibit other enzymes needed in HIV's replication (protease and reverse transcriptase).

"The development of Isentress is a significant milestone in the history of HIV/AIDS therapy because we now have a drug that's potent against another key enzyme essential for viral replication. It's important for physicians to know that Isentress should always be used in combination with other active agents," said Joseph J. Eron Jr., M.D., professor of medicine, Division of Infectious Diseases, UNC Chapel Hill School of Medicine, as quoted by Medical News Today.

The good news comes just few weeks after Merck's HIV vaccine, which has been 10 years in development, has failed in a human trial and has been canceled late September. The Phase II clinical trial has showed the vaccine was completely ineffective in protecting from a HIV infection. The Phase II trial, co-sponsored by Merck & Co., Inc., and the HIV Vaccine Trials Network, (which is funded by the National Institute of Allergy and Infectious Diseases) has involved 3,000 healthy volunteers at high risk for HIV infections.

The Phase II trial, dubbed STEP, found that from one placebo group of 762 volunteers 21 became infected with HIV, while from another group of 741 who received the experimental drug 24 became infected with HIV.

"As the AIDS crisis continues, new drugs like Isentress are needed, which target the virus in unique ways," said Ben Cheng, deputy director, Forum for Collaborative HIV Research, quoted by AP. "The HIV advocacy community is really excited and encouraged by this new treatment."