AbobotulinumtoxinA (Dysport) dosing in cervical dystonia: an exploratory analysis of two large open-label extension studies.

Treatment with botulinum toxin-A is recommended as first-line treatment for cervical dystonia (CD). In clinical practice many factors appear to influence dose adjustment and the retreatment regimen; however, there is little information available in the literature regarding the evolution of dosing over treatment cycles. We report on two similarly designed, long-term, multicenter, open-label extension studies of Dysport for the treatment of CD, which followed 500 U fixed-dose placebo-controlled trials. Both studies specified a fixed 500 U dose for the first open-label treatment cycle, with dose adjustment in subsequent treatment cycles according to the clinical response. These analyses include 218 patients who entered the two studies; doses in the subsequent treatment cycles ranged between 250 and 1,000 U. During open-label treatment, all treatment cycles resulted in improvements in mean Toronto Western Spasmodic Torticollis Rating Scale (TWSTRS) total scores. However, increasing the dose of Dysport above the initial 500 U dose was not observed to result in an incremental improvement in response as measured by the TWSTRS. No individual patient characteristic was found to reliably predict the use of higher doses at each treatment cycle. Dysport was generally well tolerated with no major differences in the incidence of adverse events (AEs) observed with different doses. Dysphagia was considered an AE of special interest and dysphagia data from the open-label studies were combined with two Phase II studies. Analysis of this enhanced database indicates that unilateral injections of >150 U into the sternocleidomastoid muscle is associated with a higher dysphagia risk. Thus, limiting the dose in the sternocleidomastoid may help reduce the incidence of dysphagia.

Immunoresistance in cervical dystonia patients after treatment with abobotulinumtoxinA.

Formation of antibodies against botulinum toxin type A has been observed following treatment of Cervical Dystonia (CD). We present the immunological findings from two 12-week Phase III prospective, randomized, double-blind, single-dose, placebo-controlled studies (Study 1, n = 116; Study 2, n = 136). Patients in both studies were administered abobotulinumtoxinA 500U or placebo intramuscularly at baseline. Patients could receive up to three or four additional treatments (250-1000U) in an open-label follow-up period. Blood samples were collected at baseline and during treatment to test for antibodies to abobotulinumtoxinA using a radioimmunoprecipitation assay (Study 2 only) and a mouse protection assay. Loss of response was predefined using the Toronto Western Spasmodic Torticollis Rating Scale (TWSTRS) total score at 4 weeks following injection. No subjects in Study 1 and one individual in Study 2 developed neutralizing antibodies (nABs) during the double-blind treatment phase; the individual who developed immunoresistance had received botulinum toxin type A treatment prior to the study and did not respond to treatment. Two subjects demonstrated a change in nAB status during open-label treatment and overall responsiveness was maintained in these patients. In conclusion, the development of immunoresistance was rare and, in the presence of circulating nABs, patients may still gain benefit from intramuscular abobotulinumtoxinA treatment.