The drug, rilpivirine or TMC278, is a non-nucleoside reverse transcriptase inhibitor (NNRTI) being developed for use in combination therapy for treating the human immunodeficiency virus (HIV) that causes AIDS.

J&J already has a deal with U.S. biotech company Gilead Sciences to develop a single pill combining rilpivirine with Truvada, a drug containing Gilead's tenofovir and emtricitabine.

Gilead currently sells a once-daily pill, Atripla, that combines Truvada with Sustiva, an older NNRTI made by Bristol-Myers Squibb. But it earns no profit on the Bristol drug, known generically as efavirenz, and all of the Atripla components lose patent protection in the next few years.

Under the deal with J&J, Gilead would keep up to 30 percent of TMC278 sales.

J&J said a combined analysis of its trials found that, after a year of treatment, 84.3 percent of HIV patients treated with TMC278 and Truvada achieved undetectable levels of the virus compared to 82.3 percent of patients treated with Atripla or similar drugs.

Fewer TMC278 patients, 2 percent, dropped out of the trials due to side effects versus 7.2 percent of the Sustiva group, according to results presented at the International AIDS Conference in Vienna on Thursday.

Serious side effects, including psychiatric and neurologic problems, were seen in 16 percent of the TMC278 group versus 31 percent of the Sustiva group.

But the data also showed 9 percent of TMC278 patients experienced virologic failure compared to 4.8 percent of Sustiva-treated patients.

HIV doctors are concerned about virologic failure -- meaning patients' HIV levels either fail to drop or rebound after an initial drop -- since it could signal the virus was mutating, making it resistant to other drugs in the same class.

The higher failure rate for TMC278 raises the question of whether Gilead would be able to switch patients from Atripla, which saw sales of $2.4 billion last year, to the new three-drug pill which has been nicknamed Btripla.

In addition to the potential TMC278/Truvada combination, Gilead is developing a Quad pill that includes a component drug belonging to a new class of medicines called integrase inhibitors, designed to block genetic information needed for HIV to reproduce.

Merck & Co already has an established integrase inhibitor called Insentress, which sold $752 million last year, and GlaxoSmithKline said on Wednesday it was moving its experimental drug, code-named '572, into late stage testing.

J&J said each of its TMC278 studies will last a total of 104 weeks but it planned to submit the 48-week findings to U.S. regulators in an application seeking approval of the drug as a treatment for previously-untreated HIV patients.

Separately on Thursday, researchers said a new AIDS drug from GlaxoSmithKline and its partner Shionogi works faster and has fewer side effects than Bristol-Myers Squibb's Sustiva.