HIV drugmaker Gilead Sciences Inc. said Thursday two of its treatments fared on par with other drugs in studies of adults with HIV infections who have not been treated.

The Foster City, Calif., company said that the tablet Stribild was not inferior after two years of treatment to two regimens seen as the standard of care for HIV. A non-inferior finding essentially means that the drug did not show superiority or inferiority to the other treatments in the study.

Stribild combines four compounds into a daily tablet. The U.S. Food and Drug Administration approved it last August for use in treating HIV-positive adults who have yet to receive treatment. European regulators are currently reviewing the drug.

Barclays analyst Tony Butler said he thinks the drug will receive European approval as well.

Gilead also said a separate study showed that another drug, the tablet Complera, was not inferior when compared to Atripla, Gilead's biggest seller. Complera showed a statistically significant difference in effectiveness compared to Atripla in patients with a low level of the virus and was non-inferior in patients with high levels.

Complera has already received approval in both the United States and Europe.

Citi Investment Research analyst Yaron Werber believes Complera should eventually replace Atripla over time. "This will have a dual benefit to Gilead of (1) higher margin and (2) longer patent life," the analyst wrote in a note.

Morningstar analyst Karen Andersen said Gilead was aiming to show that the drugs were just as effective as established treatments but with fewer side effects.

Shares of Gilead fell 92 cents to $71.37 Thursday in morning trading while the Nasdaq exchange edged lower.