Clinicians ID botulinum toxin dose disparities

Treating facial rhytids may require botulinum toxin doses as much as five times higher in the upper facial muscles than the lower facial muscles, according to findings of a recent study.

Investigators with the University of Washington, Seattle, collected electromyography (EMG) data to assess whether the disparity between botulinum toxin doses is due to differences in muscle groups’ responses to the treatment, or to variable amounts of paralysis that is required to achieved the desired outcomes, according to the study abstract.

Researchers collected data from 24 patients before treatment with onabotulinumtoxinA, at two to four weeks and at three months after injections to the corrugator and depressor anguli oris muscles.

Investigators noted a 78 percent mean motor unit duration and 64 percent maximal amplitude reduction for the corrugator muscle, but a 54 percent mean motor unit duration and 18 percent maximal amplitude reduction for the depressor anguli oris at two to four weeks (P=2.7 x 10 ^-8 and P=1.3 x 10 ^-14, respectively). Function was partially recovered for both muscle groups at three months after injection.

“OnabotulinumtoxinA causes a similar dose-dependent reduction in mean motor unit and maximal voluntary amplitudes for muscles of the upper and lower face,” study authors noted. “The dose disparity appears to result from differences in the amount of paralysis required to achieve desirable aesthetic results.”

The study was published online Feb. 21 in JAMA Facial Plastic Surgery.