Botulinum toxin type B for dynamic glabellar rhytides refractory to botulinum toxin type A

BACKGROUND. Botulinum toxin type B (BTX-B; Myobloc) has recently been introduced for the treatment of dynamic rhytides. This serotype is structurally similar to botulinum toxin type A (BTX-A; Botox) and appears to produce equivalent muscular paralysis. Because of the fact that some patients may become resistant to the effects of BTX-A with its continued use or may require large doses of type A to exert adequate muscular paralysis, the use of BTX-B may prove beneficial in these cases. OBJECTIVE. To determine the effect of BTX-B on glabellar rhytides refractory or showing decreased clinical effect to treatment with BTX-A. METHODS. Twenty females (mean age, 43 years) with vertical glabellar rhytides showing decreased or negligible clinical effect to BTX-A were treated with intramuscular injections of BTX-B. Five standardized intramuscular sites (procerus, inferomedial corrugator muscles, superior middle corrugator muscles) received a total dose of 2,500 U. Patients were evaluated at pretreatment and 48 to 72 hours, 1 week, and 2 and 4 months after injection. RESULTS. All glabellar rhytides improved after treatment with BTX-B injections. Peak clinical effect was noted 1 month after treatment, with 50% of peak effect evident at the 2-month follow-up. Near complete dissolution of effect was seen at 4 months after treatment. Side effects were transient and were limited to moderate injectional pain and rare bruising and frontal brow tightness. CONCLUSIONS. BTX-B is an effective treatment modality for glabellar rhytides refractory or exhibiting decreased clinical effect to BTX-A. The duration of effect using the 2,500 U dosing schedule described herein was shorter than that typically achieved after equivalent BTX-A injection.