Botulinum toxin B shows rapid onset, efficacy in OAB

Montreal-Botulinum toxin type B appears to be efficacious for the treatment of overactive bladder, although the agent has a short duration of action, according to British researchers. While their small, randomized, double-blind, placebo-controlled, crossover-design study specifically examined serotype B, the researchers said botulinum toxin A is likely the preferred agent because of its greater durability.

Results were presented at the International Continence Society annual meeting here and subsequently published in the Journal of Urology (2005; 174:1873-7).

Patients' responses to the King's Health Questionnaire likewise indicated significant differences in the changes to quality of life.

Two patients developed acute urinary retention during the active phase of treatment and withdrew from the study.

Dr. Malone-Lee added that, while botulinum toxin B has a rapid onset of action (24 to 48 hours), it is very short acting, limiting its clinical applicability.

"Botulinum toxin B is limited by its duration of activity, which is about 6 weeks," he said. "Botulinum toxin A has a clear advantage because of its longer duration of action. The data can be used to encourage people to use botulinum toxin A with more confidence."

Dr. Malone-Lee emphasized the marked difference between treatment arms, despite the crossover study design, and he encouraged researchers to mount more crossover studies.

"We could detect a carryover effect during the second placebo arm; that is, among those patients who went from botulinum toxin to placebo," he said. "While there was such an effect, it doesn't cloud the difference between treatment groups. There is an astonishing utility and power in the crossover design, and I think we should be revisiting this design in our field."

Dr. Malone-Lee acknowledged that patients in the treatment arm experienced some systemic anticholinergic effects for which he was unable provide an explanation.

Caveat issued

Brigitte Schurch, MD, a member of the Spinal Cord Injury Centre at the University Hospital Balgrist in Zurich, Switzerland, raised the issue of potential cross-reactivity with the more commonly used botulinum toxin type A in patients who are initially administered botulinum toxin type B. Because of cross-reactivity between toxins, she recommended that type B be regarded as a second-line therapy.

"If you treat your patients with toxin type B, there is the risk of immunogenicity," Dr. Schurch said during the ICS session. "There is cross-reaction between type A and type B, which means that if you treat the patients primarily with the type B, they will have no chance to be treated with another type of toxin."