MONDAY, June 20 (HealthDay News) -- A more recently approved version of botulinum toxin type A beat the anti-wrinkle medication Botox in a trial that compared the respective powers of each in erasing those unwanted lines of aging around the eyes known as "crow's feet."

"One month after treatment, on a two-to-one preference basis, patients picked Dysport over the Botox in terms of wrinkle improvement," said study co-author Dr. Corey S. Maas, an associate clinical professor at the University of California, San Francisco, as well as a plastic surgeon with The Maas Clinic, based in San Francisco and Lake Tahoe.

"So, we can say that when it comes to addressing the smile lines around the eyes, the crow's feet, at one month the Dysport is more effective than Botox," Maas said. "And that's a big deal, because Botox is such a recognized household name now. And it's such a great drug. But when you have something that comes in that's as good in some areas, let alone even better, it's big news for all of us, both doctors and patients."

Maas and his colleagues report the findings in the June 20 online edition of the Archives of Facial Plastic Surgery.

In 2002, the U.S. Food and Drug Administration first approved a particular form of botulinum toxin type A; this drug is popularly known as Botox and is manufactured by Allergan Inc.

An alternate version of the same botulinum toxin was approved in Europe in 2001 for general cosmetic applications. The drug, known as Dysport, is manufactured by Medicis Aesthetics; this version of botulinum was approved for use in the United States in 2009.

To compare the efficacy of both, the research team focused on 77 women and 13 men aged 18 and up between 2009 and 2010. None had previously undergone a facelift, brow lift or laser/chemical resurfacing. None had been exposed to botulinum in any form in the six months prior to the study launch, nor had any experienced adverse side effects as a result of previous exposure to botulinum.

Pre-procedure photographs were taken of all the patients, both while at rest and while contracting their foreheads and eyebrows. Wrinkling was subsequently graded on a five-point scale.

Next, the team the launched a so-called "split face" study, in which the right and left sides of each patient's face were each exposed to one of the drugs. Calculating that the strength ratio of the two drugs is about three-to-one, the researchers injected 10 units of Botox into the crow's feet region of one side of the face, compared with 30 units of Dysport on the other, according to the report.

One month following injection, the patients were asked to contract their muscles as hard as they could, while photographs were again taken.

The result: both the researchers and a majority of patients concurred that Dysport appeared to produce a better outcome. Specifically, two-thirds of the patients expressed a preference for Dysport, ranking Dysport nearly one point higher on the five-point wrinkling scale.

The authors noted, however, that when the patients relaxed their faces there was no appreciable difference between the Dysport and Botox sides.

"Now we want to be careful not to overplay this," stressed Maas. "From our findings, it's clear that there's a better smoothing effect and clearing of lines around the eyes with Dysport. But does that also mean that Dysport is better at achieving the same thing around the mouth or forehead or neck? We really can't make that conclusion."

Maas added that, "the cost of the two amounts respectively are about the same. Maybe actually a little bit less for Dysport, but not substantially less."

He also acknowledged that although the manufacturers of both drugs were approached to support the current investigation, only the maker of Dysport ultimately contributed funding to the effort.

"And what I would personally say about that," noted Maas, "is that if you already own 90 percent of the market why would you fund a study where if you tied you lost? But I will add that Allergan didn't like the dosing or the statistical analysis we used, despite the fact that I believe the body of scientific evidence supports the way we handled both."

But Allergan issued a statement Monday that challenged the findings on several grounds, which included the small size of the study, the short length of the trial and, most importantly, the dosing ratio the researchers used when deciding how much of each product to use on the patients' faces.

"It is important to understand that no two botulinum toxins are alike and each has a unique molecular structure, formulation, potency and safety profile," the company said in its statement. "In fact, the U.S. FDA-required product labels for BOTOX Cosmetic and other botulinum toxins state that different botulinum toxin products are not interchangeable and no consistent dose ratio exists among botulinum toxin products."

"The most significant flaws in this study's design were the attempted dose conversion and injection pattern. In this study, patients were treated with 10 units of BOTOX Cosmetic and 30 units of Dysport. As stated above, BOTOX Cosmetic and Dysport are not interchangeable and there is no established dose conversion, meaning 10 units of BOTOX Cosmetic does not equal 30 units of Dysport. When patients are treated with BOTOX Cosmetic for its approved indication in the glabellar (vertical frown lines between the eyebrows), they typically receive 20 units, which is the FDA-approved dose. In addition to specific dosing regimens, BOTOX Cosmetic also has a unique injection pattern for proper administration, pending the treatment area and individual patient."

Dr. Doris Day, a dermatologist with Lenox Hill Hospital in New York City, also cautioned that the attempt to analytically stack two "very similar" drugs against one another can pose difficulties.

Commenting on the study, she said, "The problem with any study trying to compare them is that there are variations in the reconstitution measures and final numbers of units used for each drug, and that can have a large impact on the final effect of the treatment. Because these are biologics, and because there are slight differences in the manufacturing process, there will be some differences in how the final product works."

Day pointed out that both drugs are FDA-approved and have good safety track records to date.

More information

For more on botulinum toxin, visit the U.S. Department of Health and Human Services.