DEERFIELD, Ill. (AP) — Baxter International Inc. said Monday that it received an additional market approval for its drug Gammagard Liquid for weakened immune systems; it can now be used in the U.S. to treat a rare autoimmune disorder.

The Food and Drug Administration approved Gammagard Liquid as a treatment for multifocal motor neuropathy, which is marked by progressive weakness in the limbs. Baxter said the disorder affects one or two out of every 100,000 people in the U.S.

Gammagard Liquid is the first immunoglobulin treatment approved for the condition.

The drug was first approved in the U.S. in 2005 as a treatment for weakened immune systems. It was approved in Europe in 2006 under the name Kiovig. European Union regulators approved Kiovig as a treatment for multifocal motor neuropathy in June 2011.

Shares of Baxter International lost 37 cents to $51.50 in afternoon trading as the overall markets slipped.