The US Food and Drug Administration (FDA) has granted approval for Allergan's Botox (onabotulinumtoxinA) to treat lower limb spasticity in adults to decrease the severity of increased muscle stiffness in ankle and toe muscles.

The company noted that Botox is the first and only botulinum toxin product to get FDA approval to treat multiple muscle groups of the upper and lower limbs that may be impacted by spasticity.

Botox was initially approved in March 2010 to treat upper limb spasticity (ULS), or increased muscle stiffness in the elbow, wrist and fingers, in adults.

The approval is based on a large, international development programme that included a multi-centre, double-blind, randomised, placebo-controlled Phase III clinical trial that evaluated the safety and efficacy of Botox compared to placebo in more than 400 patients with lower limb spasticity following stroke.

The Phase III trial compared a total Botox dose of 300 to 400 units divided among ankle and toe muscles (n=233) to placebo (n=235).

The company noted that statistically significant improvements were observed in the two co-primary endpoints of average change from baseline in the improvement of muscle tone 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) at weeks four and six (p<0.05).

Allergan Botox global development and scientific officer and senior vice-president Mitchell Brin said: "Spasticity is a debilitating condition that can have a significant impact on patients' lives, compromising their ability to perform a range of daily activities.

"This FDA approval marks our continued commitment to partnering with scientists and researchers around the world to explore the potential benefits of Botox in treating specific medical conditions.

"We are pleased that through this research, we are now able to offer this treatment option for patients with lower limb spasticity."

In spasticity, there is an abnormal increase in muscle tone or stiffness of muscle, which may interfere with movement.

In the US, this condition affects about one million people and is usually caused by damage to the portion of the brain or spinal cord that controls voluntary movement.

Last April, the company secured additional FDA approval to expand the Botox label to treat adults with ULS to include the addition of two thumb muscles.

According to the company, it is not known whether Botox is safe or effective to treat increased stiffness in upper limb muscles other than those in the elbow, wrist, fingers, and thumb, or to treat increased stiffness in lower limb muscles other than those in the ankle and toes.

It is reported that treatment with Botox is not meant to replace the existing physical therapy or other rehabilitation that the doctor may have prescribed.