Botulinum toxin type F for treatment of dystonia: long-term experience.

The authors analyzed retrospectively the results of open-labeled botulinum toxin type F (BTXF) treatment for 1 year or longer in 18 BTXA-resistant patients. All patients except one primary nonresponder to BTXA improved initially with BTXF. Most patients continued to respond to BTXF for 1 year or longer, but four patients became resistant to BTXF. BTXF-resistant patients received a higher dose per treatment and a higher cumulative dose than BTXF-responsive patients. BTXF can be used for long-term treatment of dystonia. It seems prudent to limit BTX doses of all serotypes to the lowest necessary for clinical efficacy.