Gilead Sciences Inc said its four-medicine HIV pill, known as the Quad, worked as well as the company's widely used Atripla three-drug tablet in a late-stage trial.

In the trial, 88 percent of patients taking the Quad achieved reductions in levels of HIV in the blood, known as viral load, compared with 84 percent of those who received Atripla.

The HIV drug maker's shares fell 3 percent to $36.26 in early trade on Monday on Nasdaq.

"Seems like the market is reacting because the company did not release enough data on the trial so it can have something to announce when it presents the data at a scientific conference," BWS Financial analyst Hamed Khorsand said.

The company said discontinuation rates due to adverse events were comparable in both arms of the study.

"There are definitely questions as to why there are discontinuations, but they are not providing anymore reasons," Khorsand added.

The Quad — a combination of elvitegravir, an investigational integrase inhibitor, cobicistat or "boosting" agent and Truvada — is a complete once-daily, single-tablet regimen.

Gilead said it plans to seek approval for the Quad in the first quarter of 2012.

The late-stage trial for the drug includes two studies which are evaluating it versus a standard of care among HIV-1 infected adults, the company said.