September 2009

 

OPHTHALMOLOGY NEWS

 

How botulinum toxins work


   

Botulinum toxins are neurotoxic proteins produced by a specific bacteria, the Clostirdium botulinum, a group of spore-forming, anaerobic, gram-positive bacilli. There are seven serotypes, and the subsets impede the release of acetylcholine in the neuromuscular junction to various degrees. The end result is muscle relaxation and paralysis. The FDA noted injecting the drug into a muscle “may cause the affected muscle(s) to atrophy in the short term, but reinnervation of the muscle may occur as nerve transmission is restored” through new nerve ending growth. Botox was originally approved in 1989 for the treatment of strabismus and blepharospasm associated with dystonia, and in 2002 for improving the appearance of moderate-to-severe glabellar lines. In 2000, a second botulinum toxin A, Myobloc, was approved for cervical dystonia, but not cosmetic uses. Dysport is the second botulinum toxin to receive both clinical and cosmetic use approval. The FDA said relative potencies of the products differ within type and among the different types of botulinum. Clinical doses range widely, based predominantly on the size of the muscle to be treated and the amount of muscle weakness required. Botulism can occur after using these injections when the toxin is absorbed through the intestine or lungs or from a wound, the FDA cautions. The clinical use of the drugs can potentially result in iatrogenic botulism, the FDA said. “Although we may not distinguish between botulinum toxin products … we do not intend to suggest that the three licensed botulinum toxin products are interchangeable,” the FDA said. “The risk/benefit profile of Botox is unique to the product because no two botulinum toxins are alike,” said Mitchell F. Brin, M.D., senior vice president of global development and chief scientific officer for Botox, Allergan. Among the botulinum toxins of the same subtype, manufacturing variations can result in differences in the product’s characteristics, he said, including formulation. “Because of these differences, each botulinum toxin also has distinct dosing requirements,” Dr. Brin said.

How botulinum toxins work How botulinum toxins work
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