Prolonged Antipruritic Effect of Botulinum Toxin Type A on Cowhage-induced Itch: A Randomized, Single-blind, Placebo-controlled Trial

Botulinum toxin type A (Botox(®)) is thought to have antipruritic effects through inhibition of pruritic factors, including acetylcholine, substance P, and glutamate. The aim of this randomized, single-blind, placebo-controlled trial was to test the effect of botulinum toxin type A on cowhage, a non-histaminergic model for chronic itch. Botulinum toxin type A was injected into the arm of 35 healthy subjects, with a saline control injected into the contralateral arm. Thermal sensory parameters (warmth and heat thresholds and heat pain intensity) and itch intensity after cowhage application were examined on test areas. Botulinum toxin type A reduced itch intensity, overall perceived itch (area under the curve (AUC); percentage change from baseline), and peak itch intensity compared with the control at 1 week, 1 month, and 3 months. Botulinum toxin type A had no effect on thermal thresholds or heat pain intensity. In conclusion, botulinum toxin type A reduced cowhage itch for at least 3 months, which suggests that botulinum toxin type A is a potential long-lasting treatment for localized, non-histaminergic itch. SIGNIFICANCE Severe, localized chronic itch can negatively impact quality of life and presents a therapeutic challenge. Botulinum toxin type A (BoNT/A; Botox(®)) may provide long-lasting, localized relief in certain itchy skin and neurological conditions; however, its effects in chronic (histamine-independent) itch pathways in healthy subjects has not been elucidated. This study utilized cowhage, a plant that induces non-histaminergic itch, to determine the effects of botulinum toxin type A on temperature and itch sensation in healthy subjects. It was demonstrated that botulinum toxin type A reduced itch for at least 3 months. These results suggest that botulinum toxin type A has potential for long-lasting itch relief in localized, chronic itch states.