Dose-response relationship between the H-reflex and continuous intrathecal baclofen administration for management of spasticity.
OBJECTIVE
To determine the relationship between the H-reflex (H/M ratio) and continuous intrathecal baclofen (CITB) dose after pump implantation for control of spastic hypertonia.


METHODS
Soleus H-reflexes were serially recorded in 34 subjects (19 men, mean age 32 years, mean follow-up 1.7 years) during simple continuous mode of CITB delivery. Different fitting methods were explored to determine which function best described changes in H/M ratio with increasing CITB dose. We then calculated effective CITB doses yielding H/M ratios equal to 75, 50, and 25% (ED75, ED50, ED25) of the baseline recorded before the implant in 22 subjects.


RESULTS
We found a significant dose-response relationship between the soleus H/M ratio and CITB dose. A two-decay exponential function was the best fit on each side for pooled data, but a general linear model when controlling for subject. The mean ED75, ED50, ED25 were 30, 70, and 110 mcg/day. Logistical regression predicted with high probability that the H/M ratio should be less than 30% at CITB doses above 150 mcg/day.


CONCLUSIONS
H/M ratio is strongly dependent on CITB dose. It sharply decreases up to 150 mcg/day of CITB followed by a plateau.


CONCLUSIONS
Establishing the relationship between the H/M ratio and CITB dose may be useful for dose titration and early identification of an ITB system malfunction.
Stokic
Dobrivoje S
DS
Center for Neuroscience and Neurological Recovery, Jackson, MS 39216, USA. dstokic@mmrcrehab.org
Yablon
Stuart A
SA
Hayes
Antonio
A
Vesovic-Potic
Vladislava
V
Olivier
Jake
J
D000293:Adolescent; D000328:Adult; D001418:Baclofen / Q000008:administration & dosage*; D005260:Female; D006181:H-Reflex / Q000187:drug effects*; D006801:Humans; D015918:Infusion Pumps, Implantable; D007278:Injections, Spinal; D008297:Male; D008875:Middle Aged; D009046:Motor Neurons / Q000187:drug effects / Q000502:physiology; D009125:Muscle Relaxants, Central / Q000008:administration & dosage*; D009128:Muscle Spasticity / Q000188:drug therapy* / Q000503:physiopathology*; D018482:Muscle, Skeletal / Q000294:innervation
D009125:Muscle Relaxants, Central; D001418:Baclofen