Merck & Co. Inc. announced today that it is seeking FDA approval for the drug Isentress to be used in patients who have not received any previous medication for HIV.

Isentress already is approved by the Food and Drug Administration for use in combination with other antiretroviral agents in adult patients who had received previous HIV medications.

The drug inhibits the integrase enzyme from allowing the virus to replicate and infect new cells.

Merck, based in Whitehouse Station, N.J., has operations in the Philadelphia region.