Health authorities in the United States say they are investigating reports of serious side effects linked with treatments involving Botox.
The Food and Drug Administration (FDA) says they have received some reports of serious adverse events linked with Botox, Botox Cosmetic, and Myobloc.
The three drugs contain small doses of botulinum toxin; Botox which contains botulinum toxin type A, is approved to treat eyelid spasms, neck spasms, and excessive sweating, along with Botox Cosmetic, which is used to treat facial frown lines.
Myobloc, which contains botulinum toxin type B, is approved to treat neck muscle spasms in adults.
The most serious cases involved children treated for spasticity in their limbs associated with cerebral palsy; this is not an FDA-approved use of botulism toxins in children or adults.
It appears the adverse reactions were related to the spread of the toxin to areas distant from the site of injection, and mimic symptoms of botulism, which may include difficulty swallowing, weakness and respiratory problems.
Although no adult deaths have been linked to the drugs, some adults have been hospitalized, including at least one person who used Botox for cosmetic uses and there have been reports of adults experiencing symptoms such as difficulty holding up their heads, weakness, difficulty swallowing, and droopy eyelids.
The FDA says it is not withdrawing the drugs, but is reviewing the products' labels and is advising patients and caregivers to watch for possible side effects including weakness, difficulty breathing, difficulty swallowing, and change in voice; these effects have been reported as early as one day and as late as several weeks after treatment.
While no defects have been found in the drugs, the cases involve both approved and unapproved uses of the drugs and the suspicion is that overdosing may be to blame.
A safety data review from clinical studies submitted by drug manufacturers is being currently carried out by the FDA along with post-marketing adverse event reports and medical literature.
The FDA will publish its conclusions, final recommendations, and implement regulatory actions if they are needed, when the review is completed.
The FDA is not advising health care professionals to discontinue prescribing these products.
The FDA says the early communication is in keeping with the agency's commitment to inform the public about its ongoing safety reviews of drugs.