The FDA has approved Botox (onabotulinumtoxinA, Allergan) for the treatment of lower limb spasticity in adults to reduce the severity of increased stiffness in ankle and toe muscles. Botox is the only botulinum toxin product to be cleared by the FDA for the treatment of multiple muscle groups of the upper (elbow, wrist, fingers, and thumb) and lower limbs that may be affected by spasticity.
Botox was first approved for the treatment of upper limb spasticity (ULS), or increased muscle stiffness in the elbow, wrist, and fingers, in adults in March 2010. Additional FDA approval was received in April 2015 to expand the Botox label for the treatment of adults with ULS to include the addition of two thumb muscles.
It is not known whether Botox is effective or safe for the treatment of increased stiffness in upper limb muscles other than those in the elbow, wrist, fingers, and thumb, or for the treatment of increased stiffness in lower limb muscles other than those in the ankle and toes. Botox has not been shown to help patients perform task-specific functions with their upper limbs or to increase movement in joints that are permanently fixed in position by stiff muscles. Treatment with Botox is not meant to replace a patient’s existing physical therapy or other rehabilitation that a physician may have prescribed.
Spasticity is a condition in which there is an abnormal increase in muscle tone or stiffness, which may interfere with movement or be associated with discomfort. Affecting approximately 1 million people in the U.S., spasticity is usually caused by damage to the portion of the brain or spinal cord that controls voluntary movement. The most common causes of spasticity include stroke, adult cerebral palsy, multiple sclerosis, traumatic brain injury, spinal cord injury, physical trauma, and infection.
The FDA’s approval was based on results from a phase 3, multicenter, double-blind, randomized, placebo-controlled trial in which the safety and efficacy of Botox were compared with that of placebo in more than 400 patients with lower limb spasticity following stroke. The study compared patients treated with a total Botox dose of 300 to 400 units divided among ankle and toe muscles (n = 233) with patients given placebo (n = 235). Statistically significant improvements were observed in the two coprimary endpoints of the average change from baseline in the improvement of muscle tone, as measured by the Modified Ashworth Scale (MAS) ankle score, and the clinical benefit for patients, as assessed by the Clinical Global Impression of Change by Physician (CGI-P) score at weeks 4 and 6 (P < 0.05). The most common adverse events in the Botox group included arthralgia (3%), back pain (3%), myalgia (2%), upper respiratory tract infection (2%), and injection-site pain (2%).
Source: Allergan; January 22, 2016.