LAS VEGAS Dr. Gary D. Monheit's ideal cosmetic neurotoxin would have a rapid time of onset and a stable pharmacologic action throughout its time of activity.
Its effect would also be limited to the muscle sites of injection. "There are many variables that we put into this formula, such as the dilution we give it, the force of injection, and our injection points," he said at the annual meeting of the American Society of Cosmetic Dermatology and Aesthetic Surgery. "But we would like to have a toxin that stays stable where we're injecting it."
Other ideal properties include limited yet controlled diffusion or "the field of effect," few drug-related side effects such as pain or flulike symptoms, a natural-appearing response, and a prolonged action, "something greater than 6 months," he said.
At the present time no cosmetic neurotoxin meets all of these ideal properties, said Dr. Monheit of the departments of dermatology and ophthalmology at the University of Alabama at Birmingham. To date, Botox (Allergan Inc.) is the only cosmetic neurotoxin approved by the Food and Drug Administration, but Reloxin (known as Dysport in Europe and manufactured by Ipsen) is likely to enter the market this year.
It's difficult to directly compare Botox and Reloxin because the dosage units are registered differently (3:1 vs. 2.5:1, respectively), but Dr. Monheit maintained that the potency of the products "is essentially the same. The more units you put in of either, the more potent and the more the action is. But you have to look at each one of these [products] as a different drug. You can't truly convert back and forth because there is no direct scale to compare the units."
Because Botox is a heavier molecule than Reloxin (900 kd vs. 500600 kd), some clinicians have presumed that Reloxin would tend to diffuse or migrate from the site of injection, leading to more adverse reactions than are seen with Botox. However, this presumption did not pan out in the phase III clinical studies of Reloxin.
"Diffusion is not relevant," commented Dr. Monheit, who was a clinical investigator for the Reloxin studies. "Spread or field of effect is dependent on dosage, dilution, and technical infection variables. Clinical data supports safety and efficacy at correct dosage and technique."
The phase III clinical trials of Reloxin demonstrated that the product's onset was in 23 days but occurred as soon as 24 hours for others. The average duration was 118 days.
Another neurotoxin in the pipeline is Xeomin, manufactured by Merz Pharmaceutical. One vial of the product contains botulinum neurotoxin type A free of complexing proteins, human serum albumin, and sucrose.
Xeomin is approved for use in Germany, and phase III clinical trials are currently underway in the United States. "Hearing Europeans who've used it, it seems very similar to Botox in its effect," said Dr. Monheit, who practices dermatology in Birmingham.
PurTox (Mentor Corp.) is also being investigated. This neurotoxin contains botulinum neurotoxin type A, yet it lacks the surrounding hemagglutinin protein complex. Phase II trials in the United States demonstrated that the end points of efficacy, safety, and longevity were similar to that seen with Botox for glabellar rhytides. "Its onset seems to be similar to Reloxin, while its activity is similar to Botox," Dr. Monheit said.
Phase III trials of PurTox in the United States began in July 2007.
Dr. Monheit reported that he is a consultant and clinical investigator for several pharmaceutical companies including Allergan, Ipsen, and Mentor Corp.
'There are many variables … but we would like to have a toxin that stays stable where we're injecting it.' DR. MONHEIT