Why Dosing Matters: A Closer Look at the Dose–Response Relationship With OnabotulinumtoxinA

ABSTRACT Background OnabotulinumtoxinA is licensed in many countries for simultaneous treatment of three areas of the upper face: glabellar lines, 20 U; lateral canthal lines, 24 U; and forehead lines, 20 U. Aims To assess the onabotulinumtoxinA dosing science and dose–response relationship in the treatment of upper facial lines (UFL). Methods Key practical questions are addressed using available data. Results OnabotulinumtoxinA doses were selected for Phase 3 registrational trials based on rigorous dose‐ranging studies. In clinical practice, it is important to consider the relationship between dose and efficacy outcomes, duration, and safety. Interstudy comparison of duration analyses is complicated by the lack of a single comprehensive definition, but trial data with standard onabotulinumtoxinA dosing in the glabella suggest a median effect duration of ~4 months. Treatment of UFL at below the approved dose is associated with a shorter duration, inferior response rates, and lower patient satisfaction; there is no evidence that underdosing reduces adverse event risk. It may therefore be advisable to avoid going below the licensed dose unless there is a clear clinical rationale. By contrast, there is growing evidence that treatment outcomes can be further improved using doses above those currently licensed, without adversely affecting safety—as demonstrated in the glabella. Further studies are needed to assess this in lateral canthal and forehead lines. Additional work is also required to examine potential ceiling doses and better understand the dose–response relationship in patient subgroups. Conclusions Appropriate dosing of onabotulinumtoxinA is essential for maximizing benefit and ensuring patient satisfaction.