The U.S. Food and Drug Administration has approved an immune globulin product called Gamunex for the treatment of chronic inflammatory demyelinating polyneuropathy (CIDP), a rare autoimmune disorder characterized by progressive weakness and impaired sensory function in the legs and arms.

The FDA designated Gamunex as an orphan drug to treat CIDP. The orphan drug designation provides manufacturers with financial incentives to develop treatments for rare diseases, those affecting fewer than 200,000 people in the United States.

"This approval is part of the FDA's effort to address unmet medical needs in patients who are suffering from rare and serious diseases," said Jesse L. Goodman, M.D., M.P.H., director of the FDA's Center for Biologics Evaluation and Research.

CIDP, which affects about 25,000 people in the United States, is caused by an immune system attack on the body's peripheral nervous system. The effects of CIDP—progressive muscle weakness, loss of deep tendon reflexes, tingling, and numbness—are caused by damage to the strong, fatty material that covers and protects the nerve fibers, called the myelin sheath.

Immune globulin (antibody) products are obtained from pooled human blood plasma, which contains antibodies that fight infections. These products are often given to patients with compromised immune systems, who are at increased risk for certain infectious disease. They are also used to adjust the immune response in certain autoimmune diseases.

Researchers think it is likely that Gamunex helps improve muscle function in patients with CIDP by modulating the immune system's response to the inflammation that damages the myelin sheaths, but the exact mechanism is not known.

The FDA based its approval of Gamunex on clinical trials that showed Gamunex was effective at improving certain motor functions for up to 48 weeks after the initial treatment. Researchers used the Inflammatory Neuropathy Cause and Treatment scale (INCAT) to measure a patient's ability to perform tasks such as walking and motor tasks for the hands.

The trials showed improved CIDP patient INCAT scores for muscle function after receiving Gamunex every three weeks for a 24-week period. Twenty-eight of 59 patients treated with Gamunex had improved INCAT scores compared to 13 of 58 patients treated with placebo.

In addition, patients with improved INCAT scores participated in a follow-up trial for an additional 24 weeks. Eighty-six percent of the patients who continued to receive Gamunex maintained their improved INCAT scores compared to 61 percent of the patients who received placebo during the follow-up trial.

Adverse reactions were similar to those of other immune globulin products and included headache, fever, increased blood pressure, rash, joint pain, chills, back pain, nausea, and lightheadedness. Gamunex is manufactured by Talecris Biotherapeutics Inc. of Research Triangle Park, N.C.