Pharmacokinetic properties of different formulations of botulinum neurotoxin type A

Although the relative potency measured by the number of units per nanogram of the toxin is different for the three preparations (BOTOX = 20 U/ng; Dysport = 40 U/ng, and CS-BOT = 15.2 U/ng), the effective dose for CS-BOT is similar to that of BOTOX (Allergan, Irvine, CA). Despite the twofold difference in potency per nanogram, it appears that the clinically observable activity of 1 U of BOTOX is roughly equivalent to 3 U of the Dysport (Inamed, Santa Barbara, CA) product. Using quantitative analysis of regional paralysis produced by local injections into the gastrocnemius muscles of mice, prior studies estimated the potency ratio between Dysport and BOTOX to be 4.2 to 1. In a single-blind, randomized comparison study of Dysport and BOTOX in 91 patients with blepharospasm or hemifacial spasm, it was found that 4:1 dose ratio produced similar benefits. A similar 4:1 Dysport:BOTOX ratio was found to produce equivalent beneficial effects in a double-blind study in patients with blepharospasm, but the frequency of side effects, particularly of ptosis, was lower in the BOTOX group. In a study of 73 patients with cervical dystonia treated either with Dysport or BOTOX, it was concluded that a 3:1 ratio provides equivalent results. But a recent study concluded that the appropriate conversion factor between BOTOX and Dysport is less than 3. Therefore, there is some controversy about the relative potencies of the two preparations, with one study proposing that 1 unit of BOTOX corresponds to 1 unit of Dysport.