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FDA Eyes Safety of Allergan's Botox

The agency is primarily looking at the off-label use of the wrinkle reducer in children.

The Food and Drug Administration launched a safety review into

Allergan's

(AGN) - Get Allergan plc Report

Botox wrinkle reducer and Solstice Neuroscience's similar product, Myobloc, based on reports of serious reactions in certain patients.

The review, which primarily relates to a use for the products that hasn't been approved by the FDA, sent shares of Allergan sliding 6% Friday. The news also hit shares of

Medicis

(MRX)

, which has Reloxin, a potential competitor to the popular wrinkle-reducer, in the FDA-review process

The FDA said on a media call Friday that it's specifically concerned with off-label use of the products to treat children with cerebral palsy-associated limb spasticity. The agency is investigating whether the products, which contain botulinum toxin, led to cases of botulism that spread to parts of the body away from the injection site.

Symptoms of botulism, which can be a deadly illness, emerged in patients at a wide range of doses, the FDA said, with the most serious instances leading to hospitalization or death.

Based on post-marketing reports, the FDA said it's talking about "a relative handful" of patients in a large, but undefined, population.

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"We're relying on numbers we've generated; the company's numbers are probably different," said Russell Katz, the FDA's neurology chief. The regulator has asked the companies to submit their databases of such reports so that it can get a clearer picture of what's happening.

Allergan said Friday that as a next step it will continue to work closely with the agency, providing all of the necessary information.

"We fully support the Agency's ongoing evaluation of the safety information they receive on our product," the company said.

One concern, the FDA said on the call, is that the risk might not be included in the products' labeling. Current labeling for the products includes a warning for those with neuromuscular conditions, but the agency said that cerebral palsy and spasticity aren't considered neuromuscular disorders.

Botulinum toxins are widely used for these purposes, but because the safety issue applies to a non FDA-approved use, there isn't an established dosing regimen. Thus the agency said it's hard to know if children are getting the right dose.

"The use of Botox for the treatment of JCP (juvenile cerebral palsy) is approved in about 60 countries since 1995, it is not approved in the United States and therefore we do not promote the use of Botox for this particular condition," Allergan said Friday.

In the cases of concern, the doses were typically administered in the legs and lower half of the body to increase the tone of the muscles. But the toxins then travelled to affect respiratory muscles, for instance, the FDA said.

Allergan noted that the population with juvenile cerebral palsy are extremely compromised. Therefore, "... the number of units of Botox these children receive on a per/kg basis can be significant, ranging from 100U to 700U (and often at the higher end of the dosing range) as large muscles need to be treated," the company said.

"This is naturally a very different treatment regimen than the dosing received by a healthy adult patient who receives Botox for aesthetic use, which generally ranges between 20U and 50U," Allergan said.

Last week, Allergan said reported that sales of Botox rose 24% to $339.8 million in the fourth quarter. The company predicted that 2008 sales will reach $1.37 billion to $1.42 billion.

Shares of Allergan ended down $4.01 to $63.30. Medicis shares slipped 96 cents, or 4.2%, to $21.98.