An experimental treatment for HIV developed by GlaxoSmithKline (NYSE: GSK), Pfizer (NYSE: PFZ) and Shionogi & Co. reduced the virus in hard-to-treat patients in a late-stage study, providing further support for a regulatory filing by the end of this year.

After 24 weeks on dolutegravir, 63 percent of 183 participants who had shown resistance to previous treatments had undetectable levels of the virus, the drug makers’ HIV joint venture ViiV Healthcare Ltd. said in a statement Tuesday.

The study, dubbed Viking-3, is the third of four late-stage trials to be reported this year that Glaxo plans to use in filing for regulatory clearance of dolutegravir. If approved, dolutegravir would be the second, behind Merck & Co.’s raltegravir, in a new class of HIV medicines called integrase inhibitors that work by blocking the virus’s ability to replicate.

“At ViiV Healthcare we are committed to delivering treatment options for all populations of people living with HIV. VIKING-3 was designed to address a significant medical need in one of the most difficult populations to treat – those patients who have advanced disease and have developed resistance to integrase inhibitors as well as multiple other antiretroviral agents.” said John Pottage, MD, the chief scientific and medical officer at ViiV Healthcare.

“We are encouraged by these results in integrase inhibitor-resistant patients and look forward to receiving further phase III data in treatment-experienced patients in the coming months.”

In the first of the four late-stage trials, Glaxo said in April that dolutegravir on its own suppressed the HIV virus in 88 percent of study participants, compared with Merck’s raltegravir, which quelled the disease in 85 percent of the group.

In the second study, 88 percent of patients receiving a combination of dolutegravir and two other drugs had undetectable levels of virus in their blood, compared with 81 percent of those getting Gilead Science Inc.’s Atripla, the world’s best- selling AIDS medicine

GSK operates its North American headquarters in RTP.

[GSK ARCHIVE: Check out 10 years of GSK stories as reported in WRAL Tech Wire.]

(Bloomberg contributed to this report.)