The effect of chlorzoxazone on acute pain after spine surgery. A randomized, blinded trial.
BACKGROUND
Chlorzoxazone is a muscle relaxant administered for musculoskeletal pain, and as an analgesic adjunct for post-operative pain. Chlorzoxazone for low back pain is currently not advised due to the lack of placebo-controlled trials. We explored the effect of chlorzoxazone on acute pain after spine surgery.


METHODS
One hundred and ten patients were randomly assigned to 500 mg oral chlorzoxazone or placebo in this blinded study of patients having spine surgery under general anaesthesia. In the 4 h trial period analgesia consisted of IV patient-controlled analgesia (morphine bolus 2.5 mg). Primary outcome was pain during mobilization (visual analogue scale) 2 h after the intervention. Secondary outcomes were pain at rest, opioid consumption, nausea, vomiting, sedation and dizziness.


RESULTS
For pain during mobilization 2 h after intervention, there was no significant difference between groups: 51 (21) vs. 54 (25) mm in the chlorzoxazone and placebo groups, respectively, mean difference 3 mm (95% CI -8 to 10), P = 0.59. For pain during mobilization and at rest (wAUC 1-4 h), there were no significant differences between groups. There was no significant difference in total IV morphine use 0-4 h: median 10 (7-21) vs. 13 (5-19) mg in the chlorzoxazone and placebo groups, respectively, P = 0.82. We found no significant difference in adverse effects.


CONCLUSIONS
No analgesic effect of single-dose chlorzoxazone was demonstrated in patients with acute pain after spine surgery. Based on these findings, chlorzoxazone cannot be recommended for immediate treatment of acute pain after such procedures.
Department of Neuroanaesthesiology, Rigshospitalet - Glostrup, Copenhagen University Hospital, Glostrup, Denmark.
R V
RV
Nielsen
Department of Neuroanaesthesiology, Rigshospitalet - Glostrup, Copenhagen University Hospital, Glostrup, Denmark.
J S
JS
Fomsgaard
Department of Anesthesiology, Nykøbing Falster Hospital, Nykøbing, Denmark.
H
H
Siegel
Department of Neuroanaesthesiology, Rigshospitalet - Glostrup, Copenhagen University Hospital, Glostrup, Denmark.
R
R
Martusevicius
Department of Anesthesiology, Zealand University Hospital, Koege, Denmark.
O
O
Mathiesen
Department of Anesthesiology, Bispebjerg Hospital, Copenhagen University Hospital, Copenhangen, Denmark.
J B
JB
Dahl
D059787:Acute Pain / Q000188:drug therapy*; D000328:Adult; D000368:Aged; D016058:Analgesia, Patient-Controlled; D002753:Chlorzoxazone / Q000627:therapeutic use*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009125:Muscle Relaxants, Central / Q000627:therapeutic use*; D010149:Postoperative Pain / Q000188:drug therapy*; D011446:Prospective Studies; D013131:Spine / Q000601:surgery*
D009125:Muscle Relaxants, Central; D002753:Chlorzoxazone