[Dose-response relationship in the treatment of cervical dystonia with botulinum toxin type A (AGN 191622)--a phase II study].

Injection of botulinum toxin type A has been the treatment of choice for spasmodic torticollis for several years. Although previous reports demonstrate its effectiveness and safety, the treatment strategy has been empirical. The present study, using the freeze-dried crystalline botulinum toxin type A (AGN 191622; Allergan Inc., Irvine, CA), aimed to compare the efficacy among three treatment groups divided into low, medium and high dosage levels. Fifty-one patients who entered the study were grouped into low-dose (60 units/session), medium-dose (120 units/session) and high-dose (240 units/session) groups. Two patients (one in low-dose group and the other in high-dose group) were excluded from the assessment of efficacy because they dropped out in the early phase of the study. One experienced worsening of an existing psychosis and the other developed an acute respiratory infection. Injection sites were decided individually by palpation. If the clinical response was not satisfactory four weeks after an injection, the patient was re-injected with the same dose of toxin. The follow-up period was 14 weeks from the initial injection. The results showed that the high-dose group improved more than the other groups in the parameters of severity of symptoms and subjective benefit (p = 0.000). Also, fewer injections were required in the high-dose group to achieve substantial clinical benefit. Although the mean reduction in Tsui's score was not statistically significant among the groups, the "marked improvement" was seen more frequently in the high-dose group (p = 0.033). Unfavorable adverse effects including excessive weakness and dysphasia were always mild and transient.(ABSTRACT TRUNCATED AT 250 WORDS)