The simple dose conversions used for today's neurotoxins may not result in optimal cosmetic outcomes, and this may be due to the unique nature of each individual toxin, according to a recent study.
Currently, there are several toxins approved for cosmetic use in the United States. Though Botox (onabotulinumtoxinA, Allergan) remains the universal comparator, Dysport (abobotulinumtoxinA, Medicis) and Xeomin (incobotulinumtoxinA, Merz Aesthetics) continue to vie for the top spot in aesthetic surgery.According to Dr. Narurkar, there is little literature about head-to-head comparative studies between the toxins available, and studies that do exist are sponsored by the manufacturers. Therefore, the results may be viewed as biased.
"All studies are great, but the problem is that if they are sponsored, the credibility factor is less than if something is completely unsponsored," Dr. Narurkar explains, adding that "this remains one of the central issues regarding the true efficacy of a given neuromodulator."
NONSPONSORED STUDY Dr. Narurkar and Marguerite Germain, M.D., recently conducted an independent, nonsponsored, head-to-head study between Botox and Dysport in patients who had been previously treated with onabotulinumtoxinA and who had positive results (with doses ranging from 20 to 60 units in the glabella and 20 to 30 units in the periorbital area).
The objective of the study was to determine whether there is a simple dose conversion between the two toxins and whether there is interchangeability among them. The study included 30 patients who had all been treated with onabotulinumtoxinA in the glabella and periorbital area but had not received any toxin, filler or cosmetic treatment for six months or longer. Patients were randomized in the study to three different dose conversions of either toxin — namely, 2.5-to-1, 3-to-1 and 4-to-1.
Injection patterns were followed per protocol for both toxins in areas (five-point injection for the glabella and three to four injections for each side of the periorbital area).
Assessment was made using standardized photography at rest and at animation using the standardized Merz scale for rhytids. Assessment photographs were taken at baseline, day two, one week and at monthly intervals for four months, and onset of action of toxins was documented at visits on day two, five, seven and 10. Evaluations included onset of action, complete effect and longevity.
Results demonstrated much variation in the dose conversions in terms of satisfactory results for both the glabella and periorbital areas treated. Dr. Narurkar says the dose ranges for the glabella required at least a 3-1 (40 percent of patients) or 4-1 (100 percent of patients) ratio to achieve a satisfactory cosmetic outcome, and that the 2.5-1 ratio (20 percent of patients) could not accomplish satisfactory cosmetic results in study patients.
In addition, browlifting appeared more consistent in the onabotulinumtoxinA group compared to the abobotulinumtoxinA group, he says.
In the split-face evaluation for the effects of abobotulinumtoxinA compared to onabotulinumtoxinA on crow's feet (using the same dose conversions of 2.5-to-1, 3-to-1 and 4-to-1), Dr. Narurkar says the majority of patients (80 percent) demonstrated equivalent results at the 3-1 dose conversion ratio, compared to the 2.5-1 (20 percent) and 4-1 (100 percent) ratios.
"We found that the commonly used dose conversions between Botox and Dysport (1 unit:2.5 units) are not real," Dr. Narurkar says. "Simple dose conversions with these toxins do not work across all patients, as seen in our results."
It is popularly believed and largely accepted that the dose conversions used between Botox and Dysport work in terms of achieving a similar or even equivalent efficacy, onset of action and longevity of results. However, though both Botox and Dysport are effective in their own right, the differences seen among them in relation to the doses used can achieve different cosmetic outcomes and varying levels of satisfactory aesthetic outcomes, Dr. Narurkar says.
"Physicians should view Botox as Botox and Dysport as Dysport and use the appropriate and designated doses for each of these toxins," he says.
"Biologics are not interchangeable, and the results of our study underscore the need for more science-based trials comparing these two toxins and any new and emerging toxins that may soon become available on the market," Dr. Narurkar adds.
Dr. Narurkar is a consultant for Allergan, Galderma, Medicis, Merz Aesthetics and Revance. He has performed clinical trials for Allergan, Myoscience, Palomar, Philips, Photocure, Solta and Zeltiq CoolSculpting.