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 Monheit |
Neurotoxins PurTox (Mentor Corp.), Xeomin (Merz Pharmaceutical), and, most imminently, Reloxin (Medicis), all appear to be making their way to the U.S. market to give Allergan's Botox a run for its money. But, so far, few true standout attributes have emerged among the products to set any apart from the current gold standard.
The most extensively studied is Reloxin, currently marketed in Europe as Dysport, with phase III clinical trials performed on 2,300 patients and more than 4,800 treatments. The trials looked at factors including the onset of action, the extent of action, or the diffusion, the duration of the product's efficacy and safety.
The rates of adverse events between Reloxin and Botox were generally the same, as was diffusion, and the studies took into account the effects of multiple treatments and treatment cycles, says Gary Monheit, M.D.A Question of Efficacy
"The treatment cycles were looked at because one of the big worries concerned neutralizing antibodies — whether there are more or less of them and whether they will affect the efficacy of the drug as it is used repeatedly with people year after year," says Dr. Monheit, associate clinical professor of the Departments of Dermatology and Ophthalmology at the University of Alabama, Birmingham, Ala.
The trials looked at as many as five treatment cycles of Reloxin and found no differences in efficacy or adverse events. In fact, the researchers found that adverse events seemed to get better as the treatment cycles went on, Dr. Monheit says.
Interestingly, the onset of action was one area in which there could be a difference, with Reloxin appearing to kick in a little earlier than Botox, Dr. Monheit adds.
"Subjects were asked when they first noticed that the [Reloxin] appeared to be working and 50 percent said as early as day two and 70 percent said day three," he explains. "We've always thought the onset of action with Botox was more like about five to seven days, but those studies were never done for Botox and we really don't know for sure if that was an accurate assessment."
The duration of Reloxin's efficacy appeared to be slightly shorter in men than women, but a variable dose study comparing 60, 70 and 80 units in men with 50, 60 and 70 units in women showed duration to level out. "The response curve clearly had to do with individualizing the dosage to the patient's muscle mass," Dr. Monheit says.
The individualizing factor also may come into play in regard to treatment with Botox and other toxins.
Conversion Rate
The basic conversion of rate 2.5 to 1 was used in studies conducted in the U.S. and Europe, but that rate simplified matters when more variables should be considered in the conversion, Dr. Monheit emphasizes.
"Even though we would like to say we could make a one unit conversion to another, it is something that is difficult to do because the units are simply different," he says.
"I think that rather than talk about the units, one has to understand what the details are of the ideal doses used by Ipsen in the various different sites that have been tested."
The bottom line for conversion as well as the dose rate may be to aim for an appropriate range, rather than a specific rate, based on factors including gender, muscle mass and the area of injection.
"We've done this in clinical practice with Botox, but it's never really been studied statistically," Dr Monheit says. "The key is that we shouldn't cookbook our neurotoxin, whether it's Reloxin or Botox. It should be individualized and every patient during the exam should frown or move whatever muscles that will be injected so we can see what the muscle mass is and provide the correct dosage."
