Phase IV study comparing incobotulinumtoxin A and onabotulinumtoxin A using a 1:1.5 dose‐conversion ratio for the treatment of glabellar frown lines

BACKGROUND: IncobotulinumtoxinA and onabotulinumtoxinA are effective treatments for glabellar frown lines, and a dose of 20 U is recommended for both preparations. However, debate continues over using the same dosages of these products, although a 1:1 dose ratio has been proven in several head-to-head clinical trials in neurological and esthetic indications. OBJECTIVES: To investigate whether a 50% higher dose of onabotulinumtoxinA was nonsuperior to incobotulinumtoxinA in the treatment of glabellar frown lines in the short and long term. METHODS AND MATERIALS: Subjects aged 18-65 years with symmetrical moderate-to-severe glabellar frown lines (score: ≥2 on a validated Merz 5-point scale) at maximum frown were enrolled. Corrugator muscles on both sides were treated with two injections of either 4 U incobotulinumtoxinA or 6 U onabotulinumtoxinA (equivalent to 20 and 30 U, respectively, if corrugator muscles on both sides and the procerus are treated) allowing intra-individual comparison. Glabellar frown line severity was assessed from standardized photographs every 4 weeks for 4 months and, in a subset of subjects, for up to 6 months posttreatment. The primary efficacy endpoint was the percentage of subjects with an improvement of ≥1 point on the 5-point scale at week 4. Nonsuperiority was assessed by comparing the response rates of each product. RESULTS: Nonsuperiority of a 50% higher dose of onabotulinumtoxinA to that of incobotulinumtoxinA was confirmed at 4 weeks, 4 months, and 6 months posttreatment. CONCLUSION: There is generally no reason to increase the dose of either incobotulinumtoxinA or onabotulinumtoxinA above the 20 U recommended for glabellar frown lines.