A new once-daily AIDS drug from GlaxoSmithKline and its partner Shionogi <4507.T> proved as effective as Merck & Co's twice-daily rival product Isentress in a late-stage clinical trial.

Both the new drug dolutegravir and Isentress are so-called integrase inhibitors, a new class of drugs for fighting AIDS that are designed to blocks the HIV virus from entering cells.

GSK and Shionogi said on Monday that their experimental drug dolutegravir showed non-inferiority to Isentress, or raltegravir, when given for 48 weeks alongside two older types of HIV/AIDS medicines.

In total, 88 percent of study participants on once-daily dolutegravir had their virus suppressed against 85 percent of those on twice-daily Isentress.

Merck's drug, which had sales of $1.4 billion (876 billion pounds) last year, is currently the only integrase inhibitor approved by regulators. In addition to GSK/Shionogi, Gilead also has a rival product in Phase III testing called elvitegravir.

(Reporting by Ben Hirschler)