It would be a great idea for a pharmaceutical company to develop a longer acting botulinum toxin!
Currently, there are three on the market that are approved in the United States for treatment of dynamic rhytides. They are Dysport, Botox, and Xeomin. Depending upon who you speak to, these toxins have variable durability. In my experience, Dysport and Botox tend to last a shade longer than Xeomin does, however double-blinded placebo controlled studies do not support this observation and are generally deemed equivalent to one another. As of today, there is no botulinum product that lasts greater than six months for dynamic wrinkles.