Amgen said on Tuesday that its drug helped improve daily activities including chewing and swallowing in patients suffering from a rare muscle-weakening disease, meeting the main goal of a late-stage study.

The drug, inebilizumab, was tested in patients suffering from myasthenia gravis, which is caused by an abnormal immune reaction that weakens the muscles that control the eyes, mouth, throat and limbs.

Inebilizumab, also known as uplizna, belongs to a class of drugs that target a protein, called CD19, present on immune cells.

Myasthenia gravis is estimated to affect about 36,000 to 60,000 people in the United States, according to the Myasthenia Gravis Foundation of America.

Separately, the drugmaker also said its experimental drug, rocatinlimab, met the main goals and secondary goals in a late-stage study that tested it as a treatment for an inflammatory skin condition known as atopic dermatitis.

Shares of the drugmaker fell about 2% to $325 in extended trading.

Last year, the U.S. Food and Drug Administration approved Netherlands-based Argenx SE’s subcutaneous injection, Vyvgart Hytrulo, as a convenient treatment option for the muscle-weakening condition.

Argenx’s drug, which uses the active ingredient efgartigimod, was first approved by the FDA in 2021 as an intravenous injection.

Uplizna is unlikely to meet the high bar set by Argenx’s Vyvgart, but its once every 6-months dosing could be a potential differentiator if safety is clean, TD Cowen analyst Yaron Werber said in a note ahead of the results.

Uplizna — if approved for myasthenia gravis — will also compete with AstraZeneca’s Soliris, another intravenous treatment.