UPDATE 2-FDA OKs widened use of Merck's Isentress HIV drug

* Isentress approved for previously untreated patients

* Merck says safety profile could be drawing card

* Merck shares little changed in after-hours trade (Adds shares)

NEW YORK, July 9 (Reuters) - Merck & Co MRK.N on Thursday said U.S. regulators had widened the approved use of its Isentress HIV treatment to include patients who have not yet been treated for infections with the virus that causes AIDS.

Isentress, the only approved member of a new family of anti-HIV medicines known as integrase inhibitors, has been available since late 2007 for patients who have failed to benefit from prior treatment with HIV medicines.

The new indication could help boost sales of the drug, which posted revenue last year of $361 million and is often used with the widely prescribed combination treatment Truvada sold by Gilead Sciences Inc GILD.O.

Isentress blocks a protein called integrase, thereby preventing genetic material from the virus from integrating with human cells. Gilead is in the process of developing a similar medicine.

Merck said Isentress was well tolerated in clinical trials -- with relatively few side effects.

Isentress and standard treatment together proved about twice as effective at suppressing HIV in clinical trials as standard treatment alone among patients who had previously failed to benefit from HIV drugs.

In separate trials among patients not previously treated for HIV, Isentress and Truvada together were slightly more effective at driving down HIV levels than Truvada combined with efavirenz -- an older Merck HIV treatment.

Merck shares were trading at $26.90 after-hours, little-changed from their closing price of $27.01 Thursday on the New York Stock Exchange. (Reporting by Ransdell Pierson; Editing by Gary Hill) (Reuters Messaging:; 646-223-6034;