Retrospective evaluation of the dose equivalence of Botox® and Dysport® in the management of blepharospasm and hemifacial spasm: a novel paradigm for a never ending story

Botox (R) and Dysport (R) are the preparations of botulinum neurotoxin most widely used for therapeutic purposes. Several studies have addressed the topic of the equivalency ratio (D/B ratio) to be used in clinical practice and whether a reliable value exists is still a matter of debate. To this purpose, we ideated a novel paradigm by retrospectively examining the patients affected by hemifacial spasm and blepharospasm. We compared the pairs of treatments with a switch from one brand to the other undergone by the same patient in consecutive sessions with overlapping clinical outcome. Out of 2006 treatments, we found 51 treatment pairs. D/B ratio was extremely variable (range 1.2-13.3) and in most cases (65%) it was between 1:3 and 1:5. In conclusion, even if the 1:4 ratio might be reliable for clinical purpose, a true bioequivalence between Dysport (R) and Botox (R) might not exist due to the intrinsic difference in their pharmacokinetic properties.