Key question 1: What is the optimal dosage for treating the glabella?
This is an important question. The glabella is probably the most frequently treated area. Fortunately there are several clinical trials available that try to answer this question. The question will be discussed for both brands separately.
What should efficacy measure? BNT targets the activity of the mimic muscles. Therefore, the ability of the toxin to reduce muscular movements should be measured. Usually it is not the muscular strength itself, but the effect of the reduction of muscular strength on the severity of wrinkles, which is measured by clinical scales. In most clinical trials four-point rating scales (with o for no and 3 for severe wrinkles) have been used to measure efficacy (Honeck et al. 2003).
In addition, subjective improvement is an important outcome measure. Here several scales have been used.
There are several trials focusing on the optimal dosage of Botox in the area of the glabella. The standard dosage used is 20 Botox U. In the first large placebo-controlled trial, patients with moderate to severe glabellar lines at maximum frown received intramuscular injections of 20 U BNT-A or placebo into five glabellar sites (Fig. 1.1). A total of 264 patients were enrolled (203 treated with BNT-A, 61 with placebo). There was a significantly greater reduction in glabellar line severity with BTX-A than with placebo (all measures, every follow-up visit; P < 0.022). The effect was maintained for many patients throughout 120 days (Carruthers et al. 2002).
The same authors investigated in a doubleblind, randomized clinical trial the efficacy, safety and duration of the effect of four dosages of BNT type A in the treatment of glabellar
rhytids in females. Eighty female subjects with moderate to severe wrinkles at maximum frown entered the study. Patients were randomly administered 10, 20, 30 or 40 Botox U in seven injection points (Fig. 1.2). Objectively, 10 U of BNT type A was significantly less effective than 20, 30 or 40 U. The relapse rate at 4 months was significantly higher in the 10-U group (83%) versus 40, 30 or 20 U (28%, 30% and 33% respectively). The authors concluded that 20-40 Botox U was significantly more effective at reducing glabellar lines than 10 U (Carruthers et al. 2005).
A similar study in male patients was published the same year. In this comparable study, 80 men were randomized to receive a total dose of either 20, 40, 60 or 80 U of Botox distributed in seven points in the glabellar and lower forehead area. The 40, 60 and 80 U dosages of BNT type A were consistently more effective in reducing glabellar lines than the 20-U dose (duration, peak response rate, improvement from baseline). There was a dose-dependent increase in both the response rate at maximum frown and the duration of effect assessed by the trained observer.
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