Dilution Volume of Botulinum Toxin Type A for the Treatment of Glabellar Rhytides

Abstract

Because well-controlled studies examining the efficacy and safety of various dilutions of botulinum toxin type A (BTX-A) have not been performed, dilutions used in clinical practice are chosen at the discretion of the clinician. The objectives were to determine the most effective BTX-A dilution for the glabellar region, the relationship between dilution and duration of effect, and the side effect profile of each dilution in women with glabellar rhytides. Eighty women with moderate-to-severe wrinkles at maximum frown were randomized to one of four dilution groups in a 48-week, single-center, double-blind, parallel-group study. Subjects received 30 U BTX-A (BOTOX, Allergan, Inc.) injected into the glabellar region at dilutions of 100, 33.3, 20, or 10 U/mL. Outcome measures included trained-observer and subject assessment of wrinkle severity at repose and at maximum muscle contraction using the Facial Wrinkle Scale (FWS) and adverse events. All dilutions of BTX-A effectively improved glabellar rhytides as assessed by both trained observers and subjects using the FWS. No significant differences on FWS scores were seen among the dilution groups by trained observers at any time point. Although a difference among groups was seen in subject-assessed responder rates, there was no obvious relationship between dilution and response. BTX-A treatment was well tolerated, and there were no significant differences between the four dilution groups in the number of subjects reporting adverse effects. In this study, the dilution of BTX-A was not critical to the success of treatment.