Equipotent doses of botulinum toxin type A products share same radius of action

September 1, 2005

The two commercially available formulations of botulinum toxin type A - Botox Cosmetic (Allergan) and Dysport (Ipsen/Inamed) - produce similar "action halos" when injected into the frontalis muscle under identical conditions to treat horizontal frown lines, says Doris M. Hexsel, M.D., private practitioner in Porto Alegre, Brazil, and former professor of dermatology, University of Passo Fundo School of Medicine, Brazil.

Dr. Hexsel performed a randomized, blinded, pilot study to compare the area of extension of action of the two products. The trial enrolled 18 volunteers, including males and females ages 19 to 49 years old, who served as their own controls. Botox (100 units per vial) was diluted in 1 ml of saline and Dysport (500 units per vial) was diluted in 2 ml of saline, resulting in a dose ratio of 1:2.5 units, which is considered equivalent in potency for many experienced physicians.

One side of the forehead was randomized to treatment with Botox 2 units/0.02 ml and the contralateral side was injected with Dysport 5 units/0.02 ml. Special care was taken to deliver both of the injections at the same depth.

After 28 days, the action halo of the botulinum toxin was measured in millimeters as the radius of the circular area of paralysis around the injection point based on patient and investigator assessments and as the halo revealed by Minor's starch-iodine test. Those evaluations showed the two products had similarly sized, regular halos of action and seemed to produce paralysis of equivalent intensity.

"The action halo represents the extension of the action area from the point of botulinum toxin injection, and it is a critical determinant of efficacy and safety. Based on knowledge of the action halo, the treatment can be designed to target the desired muscles without affecting adjacent muscles, and it can be given using the lowest dose and fewest injections necessary to optimize both therapeutic response and tolerance. With the reconstitution and administration protocol used in this study, we conclude that the equivalent doses of 1:2.5 units between Botox Cosmetic and Dysport can be administered with the same injection technique to predictably achieve similar responses," Dr. Hexsel says.

Brazil experience

The botulinum toxin type A formulation from Ipsen/Inamed is currently in phase 3 studies in the United States and will be marketed under the trade name Reloxin. Both Botox and Dysport have been available for several years in Brazil and other countries.

"We have used both agents and consider both to be good products," Dr. Hexsel says. "In our experience, they both produce the same results when used for either muscle relaxation or anhidrosis. However, different users have different opinions about their dose equivalency and area of action."

For the current study, Dr. Hexsel used a dose ratio of 1:2.5 for Botox: Dysport based on her previous experience indicating the two products produced equivalent results when used at that ratio for treating facial wrinkles. The equivalent doses were delivered in identical volumes to prevent differences in spread of the injected toxin from the point of injection, as it is known that larger amounts of fluids can spread after injection.

In addition, the protocol also aimed to standardize the orientation of the injection and to control induced bleeding, as those factors may also influence diffusion of the botulinum toxins. Each injection was delivered into the upper frontalis muscle on its assigned side of the face at a point over the middle of the pupil and 3 cm above the brow. To assure the injections were delivered at the same depth, the needles used to inject the two products on both sides were covered by the same guide (the cut cap of the needle). Bleeding was controlled with pressure application after all injections.

No diffusion seen

Dr. Hexsel notes that neither of the botulinum toxin type A products showed evidence of diffusion or dispersion in the study.