Clinical Experience of Dose Conversion Ratios Between 2 Botulinum Toxin Products in the Treatment of Cervical Dystonia

OBJECTIVES: The units of different botulinum toxin products are not identical, and the dose equivalence has been debated for several years. In the year 2000, our clinic changed the recommended botulinum toxin product from Botox to Dysport for the treatment of cervical dystonia. Based on published reports, where dose conversion ratios from 1:1 to 1:6 (Botox:Dysport) had been used, and our own clinical experience, the dose conversion ratio was set to 1:2. The objective of this study was to retrospectively monitor the used doses of each product and the subsequent clinical effect. METHODS: A retrospective study, using casebook notes from 75 patients, was done to investigate treatment doses, subjective clinical effect, and the appearance of adverse events. RESULTS: The median dose conversion ratio that had been used at the product switch was 1:2.3 (Botox:Dysport). After clinical adjustment, the ratio was 1:2.1 at the next 3 treatments. There was a tendency for a more effective treatment and more adverse events after the product switch. A follow-up was performed 6.5 years later using casebook notes from 53 of the same patients. By this time, the doses had been reduced, and the median dose conversion ratio had decreased to 1:1.7 (Botox:Dysport). The adverse events reported at this point were fewer for the patients treated. CONCLUSIONS: In this study, the most appropriate dose conversion ratio to use when switching from Botox to Dysport was 1:1.7.