Unlike type A, type B is stable at room temperature, increasing its ease of use and shelf life, according to Corey S. Maas, MD, chief of the UCSF division of facial plastic surgery and lead author of the study. He explained that Type A is supplied as a powder that must be stored frozen, and once reconstituted, refrigerated and used within a few days. The researchers noted that type B may also be appropriate for patients who do not respond to type A because they have resistant or altered target sites for the drug or have developed antibodies to type A because of frequent treatments.
According to the researchers, patients injected with type B had a more rapid onset of wrinkle reduction (within 48 hours as compared to 3-7 days for type A), but the effect did not last as long (6-8 weeks as opposed to 12-14 weeks for type A), due to the low dose studied.
Though the duration of effectiveness of the drug at higher doses is yet to be determined, type B may be particularly cost-effective for patients who need only small amounts or "touch-ups," said Maas. "Physicians using type B will be able to go to the refrigerator and draw up even a small amount, without worrying about the costs of reconstituting a new vial," he said.
Botulinum toxin B was licensed by the Federal Drug Administration (FDA) in January 2001 for treatment of cervical dystonia -- a spastic contraction of neck muscles. Like botulinum toxin A, toxin B is an artificially produced neuromuscular paralyzing agent. When either toxin is injected into the muscle, it binds to nerve endings. Once in the nerve terminal, the toxin cuts proteins so that the nerve terminal is no longer able to release a neurotransmitter called acetylcholine. Without acetylcholine, nerve impulses can no longer make muscles contract. Without muscle contraction -- in the forehead and near the eyes and mouth -- wrinkles can no longer occur in these areas, said Maas.
Types A and B are two distinct medicines and are not necessarily interchangeable for all uses, said Maas. Though more studies are needed, type B may be as effective as type A for treating face wrinkles and perhaps better adapted than type A for treating conditions of excessive sweating known as hyperhydrosis. This is because type B seems to have an affinity for the sweat and salivary gland nerve terminals that may produce dryness side effects, he explained.
In addition to use in prevention of wrinkles and treating excessive sweating, botulinum type A has been used to treat uncontrolled eye twitching, crossed eyes, muscle spasms and migraine headaches. Future studies will determine if type B can be safe and effective in treating these conditions.
The researchers noted that doses of botulinum type B (800 units) injected into the muscles of the brow, eyes and forehead were well tolerated and led to no major side effects through twelve weeks of physician follow-up. Investigators followed 67 patients were who evaluated at 1, 2, 4, 8 and 12 weeks after treatment. Further studies of botulinum type B are necessary to determine the appropriate doses for the best clinical outcomes, said Maas.
Additional researchers on this study include: Jay B. Reeck, MD, and Alexander L. Ramirez, MD, both residents in the UCSF department of otolaryngology.
Funding for this study was provided by Elan Pharmaceuticals, which manufactures Myobloc®. Maas serves as a consultant for Elan Pharmaceuticals and is a member of the scientific advisory board for the manufacturers of Botox® and Myobloc®.