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Elan's Myobloc and Allergan's Botox receive approval for cervical dystonia
Families have been eagerly awaiting this new treatment," said Valerie Levitan, Ph.D., in a recent teleconference. She was referring to botulinum toxin type B (Myobloc), a new drug made by Elan Pharmaceuticals Inc. and approved by the Food & Drug Administration in December.
Levitan is the executive director of the Dystonia Medical Research Foundation, an organization that represents 33,000 North American dystonia sufferers. Approximately 10,000 of these members have cervical dystonia (CD), a disorder that causes neck muscles to contract involuntarily. When prolonged, these contractions result in awkward positioning of the head, and shorter contractions cause spasms or jerks. Understandably, while not life-threatening, CD can profoundly affect the lives of those with the disorder.
Martha Murphy, who has had CD for 25 years, agreed. After years of pain and self-conscious feelings about her appearance, she became withdrawn and depressed. Unable to turn her head, Murphy found the simplest daily activities became chores. She summed up CD by saying, "It's like an ongoing battle with the muscles in your body."
According to Chris O'Brien, M.D., medical director of the Movement Disorders Center and v.p. of Medical Affairs at Elan, CD has historically not been adequately diagnosed or treated. "It's unfortunate that for many years [CD] was thought to be a psychological condition."
Also called spasmodic torticollis, CD has been treated with oral anticholinergics, dopaminergics, and benzodiazepines. None of these has had consistent success in alleviating the symptoms of CD, according to the Dystonia Medical Research Foundation. However, in the 1980s neurologists began injecting botulinum toxin type A (Botox, Allergan Inc.) directly into the muscles involved and found the drug was effective. By preventing the release of acetylcholine (ACH), botulinum toxin inhibited muscle contraction and thereby relieved the symptoms of CD.
There have been a couple of hitches, though. While the injection procedure sounds relatively simple, O'Brien explained that that's not actually the case. Physicians must select the appropriate target muscles and botulinum toxin dose for injection, which requires skill and experience. Also, a small percentage of patients eventually develop resistance to the type A form. Researchers have suggested this may be related to the formation of antibodies to the toxin. Because the drug is a second-line therapy for CD, after oral medications, surgery or inadequate therapy are the only remaining options for patients resistant to botulinum toxin. Enter botulinim toxin type B, the second in a line of seven types (A through G) to be used for CD.
Two phase III clinical trials have evaluated the efficacy of botulinum toxin type B in treating CD. One of the two studies, in which Murphy participated, evaluated a 10,000-unit dose (the maximum recommended dose for type B) in patients resistant to type A. The average study participant using botulinum toxin type B in both studies achieved some degree of pain and disability relief, when compared with those given a placebo.
Allergan has also reformulated its version of the type A toxin, Botox. By reducing the active ingredient to 5 ng/100 units from 25 ng/100 units, the company hopes to minimize antibody formation. Late last year, the FDA approved the product for use in cervical dystonia patients.
The new formulation of type A neurotoxin has been on the market since 1997. Botulinum toxin type B will be distributed directly to physicians, and Elan expects it will be available this month.
Jillene Lewis. Two drugs offer new relief for cervical dystonia patients. Drug Topics 2001;2:17.