FDA Approves Treatment for Rare Neurologic Disease

The U.S. Food and Drug Administration today announced that it 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.

FDA Approves First Drug for Treatment of Chorea in Huntington’s Disease

The U.S. Food and Drug Administration has approved Xenazine (tetrabenazine) for the treatment of chorea in people with Huntington’s disease. Chorea is the jerky, involuntary movement that occurs in people with this disease.

Xenazine is a new drug and is the first treatment of any kind approved in the United States for any symptom of Huntington’s disease. Currently there are no other drugs that are FDA-approved to treat chorea.

Serious side effects reported with use of Xenazine include depression and suicidal thoughts and actions. Xenazine should not be used in patients who are actively suicidal or in patients with untreated depression. Concerns about the risk of suicide are heightened in all patients with Huntington’s disease.

“Xenazine represents hope for patients and families dealing with this difficult disease,” said Timothy Coté, M.D., M.P.H., director of FDA’s Office of Orphan Products Development. “For the first time, there is a treatment that can help patients with this disease gain some quality of life.”

Huntington's disease is a rare, inherited neurological disorder affecting about 1 in 10,000 people in the United States. The disease results from genetically programmed degeneration of brain cells. The deterioration causes uncontrolled movements, loss of intellectual faculties, and emotional disturbance. Huntington’s disease is passed from parent to child through a gene mutation. Each child of a parent with the disease has a 50 percent chance of inheriting the mutation.

About 30,000 people in the United States have Huntington’s disease and another 200,000 are at risk of developing the condition. Symptoms commonly develop between ages 30 and 50. The disease progresses slowly and a person may live for another 15-20 years after the onset of symptoms.

Xenazine decreases the amount of dopamine available to work at relevant synapses in the brain. Dopamine is a chemical that communicates between certain nerve cells in the brain. In patients with Huntington’s disease, this system is overactive and results in the abnormal movements called chorea. Xenazine decreases the amount of dopamine available to interact with certain nerve cells, thereby decreasing the involuntary movements.

The effectiveness and safety of Xenazine was established primarily in a randomized, double-blind, placebo-controlled multi-center clinical trial. Patients treated with Xenazine had a significant improvement in chorea compared to patients treated with placebo. Other studies provided additional support for this effect.

The most common side effects reported by patients using Xenazine in clinical trials include insomnia, depression, drowsiness, restlessness and nausea.

While the drug has been shown to decrease chorea in the short-term, it also showed slight worsening in mood, cognition, rigidity, and functional capacity in clinical trials. Health care professionals and family members of patients taking the drug should pay attention to all of the facets of the disease.

Xenazine has been approved with a required Risk Evaluation and Mitigation Strategy (REMS) to ensure that the benefits of the drug outweigh its risks, particularly the risks of depression and suicidal thoughts and actions. REMS is a strategy to manage a known or potential serious risk associated with a drug or biological product.

The REMS includes educational materials for prescribers, pharmacists and patients (and their caregivers) to help minimize adverse effects associated with Xenazine. It also includes a Medication Guide, which informs patients and their caregivers about the risks of depression, suicidal thoughts and actions, and other side effects. The FDA requires that the Medication Guide be handed out with every prescription for the drug dispensed.

Xenazine was granted orphan drug designation by the FDA. A drug is eligible for orphan drug designation if it is intended to treat a disease or condition that affects less than 200,000 people in the United States. A drug is also eligible for orphan drug designation if it is intended to treat a disease or condition that affects more than 200,000 people in the United States, but there is no reasonable expectation that the cost of developing and making available a drug for the disease or condition will be recovered from sales of the drug.

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