UPDATE 1-FDA OKs widened use of Merck's Isentress HIV drug

* Isentress approved for previously untreated patients

* Merck says safety profile could be drawing card

By Ransdell Pierson

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 significantly 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 penetrating human cells. Gilead is in the process of developing a similar medicine.

Bach-Yen Nguyen, senior director of infectious disease clinical research at Merck, said Isentress proved impressively safe in clinical trials -- with relatively few side effects and with far less tendency to raise cholesterol than other drugs.

"HIV is a chronic disease, so it's very important that drugs are well tolerated," she said, noting Isentress' safety profile may sway doctors and patients.