I have been using Botox for cosmetic reasons since 1991. Since that time, I occasionally encounter a patient who at first responded well to Botox, but after several treatment sessions, no longer responded as well or has not maintained his/her improvement for as long as previously. Some, for example, who in the past may have enjoyed six months of correction were seeing no more than four to eight weeks of results. I have been using Dysport for about ten years already and have seen a similar phenomenon with this neuromodulator, as well.
One possible explanation that has been proposed for this problem is the development of antibodies to the injectables. In such cases, I have been switching these patients to Xeomin, a neuromodulator very much like Botox, but whose manufacturer has taken pains to strip all unnecessary excess proteins from the active molecule in order to reduce its potential to provoke antibody formation. So far, I have generally had success with Xeomin in cases where patients have been suspected of antibody formation to the other two approved agents. I definitely believe it is worth a try in these instances.