Comparison of botulinum toxin types A and B: A bilateral and double-blind randomized evaluation in the treatment of canthal rhytides

BACKGROUND. The obligate bacterium Clostridium botulinum produces exotoxins (A, B, C-1, C-2, D, E, F, G) that are serologically and antigenically distinct. All serotypes have similar neurotoxic properties resulting in flaccid muscle paralysis. Types A and B are commercially available and are used widely for the reduction of dynamic facial rhytides. Although extensive information is known about type A, type B has recently become available; however, there is a limited clinical familiarity. Some of the remaining unknown distinctions between the two subtypes are the extent of toxin diffusion from the site of injection, the onset of action, the dose equivalency, and the duration of effect. OBJECTIVE. The purpose of this preliminary double-blind study was to compare the duration of muscle paralysis and rhytid reduction of botulinum toxin types A and B. Additional relevant information was obtained, all of which can be useful in toxin selection. METHOD. Ten women, ages 28 through 60, voluntarily consented to undergo a double-blind trial and were randomly assigned to have botulinum toxin type A injected into one set of lateral canthal rhytides and toxin type B into the contralateral periocular region. Based on dose-ranging investigations performed in patients with cervical dystonia, participants received treatment at the lowest reported effective ratio of 1:50 (1 U of toxin type A to 50 U of toxin type B). Three injections of 5 U of type A (total 15 U) and three injections of 250 U of undiluted type B (total 750 U) were injected into the lateral fibers of the orbicularis oculi muscle. RESULTS. Patients were evaluated at 7, 30, 60, and 90 days. Findings were compared by the treating physician, patient self-assessment, and photographic images. CONCLUSION. All patients noted rapid and satisfactory reduction in the rhytides in both periocular areas. However, upon unblinding of the solutions at the same volumes with a 1:50 ratio, type B toxin was found to be associated with slightly more discomfort upon injection, quicker onset of action, a sensation of "tightness" of the treated area, and a briefer duration of muscle paralysis.