Lb. Pearce et al., THE MEDIAN PARALYSIS UNIT - A MORE PHARMACOLOGICALLY RELEVANT UNIT OFBIOLOGIC ACTIVITY FOR BOTULINUM TOXIN, Toxicon, 33(2), 1995, pp. 217-227
Although the LD(50) has been used to quantify the biologically active
toxin in clinical preparations of botulinum A toxin (Botox(R) and Dysp
ort(R)), a discrepancy exists between the clinical potency of equivale
nt international units Of different formulations of botulinum A toxin
for multiple clinical indications. Our laboratory previously reported
that a regional chemodenervation assay in the mouse could be utilized
to detect the difference in the potencies of the clinical preparations
of toxin [Pearce et al. (1994) Toxic. appl. Pharmac. 128, 69-77]. The
purpose of this study was to quantify the regional paralysis produced
by botulinum toxin and define a new pharmacologic/biologic unit of ac
tivity that more accurately reflects the mechanism of action of botuli
num toxin in the clinical setting. Quantal analysis of regional paraly
sis revealed that the ED(50), defined as the median paralysis unit (MP
U) for Botox(R) and Dysport(R), was 0.41 +/- 0.01 and 1.00 +/- 0.02 LD
(50) units, respectively. Differences in the potencies found in retros
pective clinical studies comparing Botox(R) and Dysport(R) were accura
tely reflected, for the first time, by the dose of toxin expressed in
terms of the MPU (median paralysis unit). The data suggested that the
MPU may be a more appropriate measure of the biologic activity in ther
apeutic formulations of botulinum toxin.