FDA Approves Immune Globulin Therapy for Difficult-to-treat Chronic Inflammatory Demyelinating Polyneuropathy

The U.S. Food and Drug Administration (FDA) announced last week that it has approved an immune globulin intravenous (IGIV) therapy 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 central nervous system is comprised of the brain and spinal cord. The peripheral nervous system includes all peripheral nerves.

The FDA designated Gamunex, manufactured by Talecris Biotherapeutics Inc. of Research Triangle Park, NC, as an orphan drug for CIDP. Orphan drug status provides manufacturers with financial incentives to develop treatments for rare diseases that affect fewer than 200,000 people in the U.S. It is estimated that CIDP affects about 25,000 people in the U.S.

"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 Goodman, MD, MPH, director of the FDA's Center for Biologics Evaluation and Research, in a statement issued by the agency.

CIDP is caused by the immune system attacking on the body's peripheral nervous system. The effects of the disease -- progressive muscle weakness, loss of deep tendon reflexes, tingling, and numbness -- are due to damage to the myelin sheath, the fatty material that covers and protects the nerve fibers.

Immune globulin products are obtained from pooled human blood plasma, which contains antibodies that fight infections. These products are often given to people with compromised immune systems, such as those with HIV, who are at increased risk for certain infectious diseases. Antibody products are also used to modulate the immune response in certain autoimmune diseases.

Researchers think Gamunex helps improve muscle function in patients with CIDP by modulating the immune system's response to inflammation that damages the myelin sheath, but the exact mechanism is unknown.

The FDA based its approval of Gamunex on clinical trials that showed it 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 patients' ability to perform tasks such as walking and manual motor tasks.

The trials showed improved INCAT scores for muscle function after patients received Gamunex every 3 weeks for a 24-week period. About half of the patients (28 of 59) treated with Gamunex had improved INCAT scores, compared with about one-quarter of patients (13 of 58) who received placebo.

In addition, patients with improved INCAT scores participated in a follow-up trial for an additional 24 weeks. Of the patients who continued to receive Gamunex, 86% maintained their improved INCAT scores, compared with 61% of those 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.

9/16/08

Source
FDA News. FDA Approves Treatment for Rare Neurologic Disease. Press release. September 12, 2008.