Botulinum Toxin Therapy for Cervical Dystonia: The Science of Dosing

Abstract

The first‐line treatment for cervical dystonia (CD) is botulinum toxin type A (BoNT‐A), which has been established as a highly effective and well‐tolerated therapy. However, this treatment is also complex and challenging to apply in clinical practice. Approximately 20% of patients discontinue therapy due to treatment failure, adverse effects, and other reasons. In addition, expert consensus recommendations are lacking to guide physicians in the optimal use of BoNT‐A for CD. Among the issues still to be clarified is the optimal dosing frequency. The generally accepted standard for intervals between BoNT‐A injections is ≥12 weeks; however, this standard is based primarily on the methodology of pivotal trials for the BoNT‐A products, rather than on evidence that it is optimal in comparison to other intervals. While some retrospective, observational studies of BoNT‐A used in clinical practice appear to support the use of ≥12‐week dosing intervals, it is often unclear in these studies how the need for reinjection was determined. In contrast, a prospective dose‐ranging trial in which patients were allowed to request reinjection as early as 8 weeks showed that about half of patients receiving abobotulinumtoxinA, at the currently recommended initial dose of 500 U, requested reinjection at 8 weeks. Moreover, results from an open‐label, 68‐week extension phase of the pivotal trial of incobotulinumtoxinA showed that 47.1% of patients had received reinjection at ≤12 weeks. Ongoing studies, such as the Cervical Dystonia Patient Registry for Observation of BOTOX® Efficacy (CD PROBE), may help clarify this question of optimal dosing intervals for BoNT‐A in CD.