DOSE-RESPONSE CURVE OF HUMAN EXTENSOR DIGITORUM BREVIS MUSCLE FUNCTION TO INTRAMUSCULARLY INJECTED BOTULINUM TOXIN TYPE-A

To develop a human model for measuring the effect of intramuscularly i njected botulinum toxin, we injected both extensor digitorum brevis (E DB) muscles in 13 healthy volunteers with seven varying doses of botul inum toxin type A. We measured, pre- and postinjection, EDB M-wave amp litude, area, and mean rectified voltage (MRV) (obtained during maxima l voluntary muscle activation), There was a logarithmic-appearing dose -response relationship between increasing doses of botulinum toxin and decline in EDB M-wave amplitude, area, and MRV. The decline was incre mentally less at higher doses of toxin and appeared to level off at a maximal effect of 85 to 90% decrement from baseline (85 to 90% ''paral ysis'') at 15 to 20 units. The peak toxin effect was present on day 6 postinjection. Measurement of EDB M-wave amplitude, area, and MRV is a simple objective method for quantifying the onset and degree of human muscle ''paralysis'' following botulinum-toxin injection.