Long-term safety, efficacy, dosing, and development of resistance with botulinum toxin type B in cervical dystonia.

Short-term studies of cervical dystonia (CD) have demonstrated botulinum toxin type B (Bot B) to be safe and efficacious at doses of 5,000 to 10,000 units, but few long-term studies have been published and the safety and efficacy of higher doses has not been established. Additionally, there are few studies describing the development of resistance to Bot B in those with and without prior resistance to botulinum toxin type A (Bot A). We reviewed our experience with 24 patients treated with Bot B for up to 64 months. Patients were treated with Bot B for 26.2 +/- 20.4 months (range, 3-64 months) with a mean treatment dose of 14,828 +/- 6,824 units (range, 2,500-28,000 units). At last follow-up, 12 patients demonstrated ongoing benefit, 8 patients had become secondarily resistant, and 4 patients were primary nonresponders possibly due to the severity and nature of their CD. Nine of the 12 continued responders and 7 of the 8 secondary nonresponders to Bot B had prior probable or definite clinical resistance to Bot A. No severe adverse events related to Bot B were seen. Treatment of patients with severe CD who continue to show a beneficial response to Bot B injections commonly requires doses of 15,000 units and rarely greater than 20,000 units. Patients may continue to respond for up to 64 months. Prior Bot A resistance may be a risk factor for the development of resistance to Bot B; nevertheless, Bot B can be a useful long-term alternative in some Bot A-resistant CD patients.