( CNN ) -- The Food and Drug Administration on Friday approved the first of a new class of HIV drugs that attacks the virus in a different way . A woman wears an AIDS ribbon at a Cape Town , South Africa , hospital where HIV patients are treated . Isentress , developed by Merck & Co. , is designed for patients who have shown resistance to current treatments . The drug has been approved for adults who already have been receiving treatment , but more testing is necessary before it is approved for new HIV patients or children , the company said in a statement . Isentress belongs to a class of drugs called integrase inhibitors . These drugs work by blocking the integrase enzyme , which helps HIV replicate by inserting its DNA into new cells . Isentress is the first drug in the class to win FDA approval . Dr. Anthony Fauci , a noted HIV expert and director of the National Institute of Allergy and Infectious Diseases at the National Institutes of Health , said the FDA 's approval `` will be most welcome in the community of physicians taking care of HIV-infected patients . '' `` Its mechanism of action is particularly important in that it blocks the ability of the virus to integrate itself into the genes of cells , '' Fauci said . `` This property of the virus to integrate is important in establishing the reservoir of virus in the body that has made it extremely difficult to eradicate HIV , even with prolonged treatment . '' Two earlier classes of anti-HIV drugs -- protease and reverse transcriptase inhibitors -- also work by blocking different enzymes involved in HIV replication . Friday 's decision by the FDA will give doctors a new tool to help patients who have developed resistance to existing drugs or who are infected with drug-resistant strains of HIV . Like protease and reverse transcriptase inhibitors , Isentress will also be prescribed for patients in combination with other drugs to maximize the number of ways the virus is being attacked . The cost of the recommended daily regimen of Isentress -- a 400 mg tablet taken twice a day -- will be comparable to protease inhibitors , with a wholesale price of $ 27 , Merck said . E-mail to a friend .
FDA approves HIV drug for use in adults with resistance to existing treatments . Isentress , by Merck & Co. , is the first of new class of drugs to get approval . More testing necessary before it is approved for new HIV patients , children . Drug works by blocking different enzymes involved in HIV replication .