Argenx (ARGX) said late Tuesday its Vyvgart drug resulted in "significant improvement" in muscle strength and physical function in phase 2 studies evaluating three myositis subtypes.

The company also said the US Food and Drug Administration has granted the drug, also called efgartigimod, fast-track designation for the treatment of primary Sjogren's disease.

Sjogren's disease and myositis are inflammatory autoimmune diseases that can have a material negative impact on a patient's quality of life.

In a phase 2 proof-of-concept study, 45.5% of Sjogren's patients treated with efgartigimod showed improved outcomes compared with just 11.1% for the placebo group, Argenx said.