Clinical differences between botulinum neurotoxin type A and B.

In humans, the therapeutic use of botulinum neurotoxin A (BoNT/A) is well recognized and continuously expanding. Four BoNTs are widely available for clinical practice: three are serotype A and one is serotype B: onabotulinumtoxinA (A/Ona), abobotulinumtoxinA (A/Abo) and incobotulinumtoxinA (A/Inco), rimabotulinumtoxinB (B/Rima). A/Abo, A/Inco, A/Ona and B/Rima are all licensed worldwide for cervical dystonia. In addition, the three BoNT/A products are approved for blepharospasm and focal dystonias, spasticity, hemifacial spasm, hyperhidrosis and facial lines, with remarkable regional differences. These toxin brands differ for specific activity, packaging, constituents, excipient, and storage. Comparative literature assessing the relative safety and efficacy of different BoNT products is limited, most data come from reports on small samples, and only a few studies meet criteria of evidence-based medicine. One study compared the effects of BoNT/A and BoNT/B on muscle activity of healthy volunteers, showing similar neurophysiological effects with a dose ratio of 1:100. In cervical dystonia, when comparing the effects of BoNT/A and BoNT/B, results are more variable, some studies reporting roughly similar peak effect and overall duration (at a ratio of 1:66, others reporting substantially shorter duration of BoNT/B than BoNT/A (at a ratio 1/24). Although the results of clinical studies are difficult to compare for methodological differences (dose ratio, study design, outcome measures), it is widely accepted that: BoNT/B is clinically effective using appropriate doses as BoNT/A (1:40-50), injections are generally more painful, in most of the studies on muscular conditions, efficacy is shorter, and immunogenicity higher. Since the earliest clinical trials, it has been reported that autonomic side effects are more frequent after BoNT/B injections, and this observation encouraged the use of BoNT/B for sialorrhea, hyperhidrosis and other non-motor symptoms. In these indications the efficacy of toxins A and B are comparable and dose ratio is 1:25-30.