Objective: To characterize long‑term dose-effect patterns for incobotulinumtoxinA, onabotulinumtoxinA, and abobotulinumtoxinA in cervical dystonia (CD) using a unified dose-effect parameter (DEff) and to compare complex‑free (CF) versus complex‑containing (CC) formulations and switchers.

Background: Sustained response to botulinum neurotoxin type A (BoNT/A) in CD can wane over time due to multiple factors, including immunogenicity. Comparative multicenter real‑world data across all three formulations are limited.

Method: International, multicenter, retrospective chart abstraction (≥7 years treatment). Patient records were assigned to CF monotherapy (incobotulinumtoxinA), CC monotherapy (onabotulinumtoxinA or abobotulinumtoxinA), or switchers. DEff integrated change in annual mean dose per muscle and clinical effect versus year 2; DEff>1.2 denoted clinically meaningful worsening. Outcomes included the proportion with DEff>1.2 at year 7 and trajectories on TWSTRS and Tsui. Doses were summarized per product; switchers were modelled around the time of switch.

Results: N=250: CF monotherapy n=27, CC monotherapy n=101, switchers n=122 (predominantly CC→CF). At year 7, DEff>1.2 occurred in 11.1% (CF), 24.2% (CC), and 24.8% (switchers). Median total product-specific doses across monotherapy were 200 units for incobotulinumtoxinA, 200 units for onabotulinumtoxinA, and 750 units for abobotulinumtoxinA. TWSTRS worsened from baseline to year 7 in CC and CC→CF groups (significant), while the smaller CF group did not reach statistical power; Tsui remained numerically more stable, with improvements in the monotherapy groups. Clinician‑documented treatment‑response changes were more frequent in CC and CC→CF than CF, most often attributed to disease progression.

Conclusion: Long‑term BoNT/A treatment in CD showed broadly maintained effectiveness across formulations, with lower rates of clinically meaningful dose-effect worsening in CF monotherapy versus CC and switchers. The DEff approach is feasible for routine‑care monitoring of response dynamics and may aid long‑term optimization; prospective validation is warranted.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/long-term-dose-effect-patterns-with-incobotulinumtoxina-onabotulinumtoxina-and-abobotulinumtoxina-in-cervical-dystonia-multicenter-real-world-analysis/