Introduction: As spinal cholinergic receptors exhibit an action against somatic pain, this effect could be potentiated by intrathecal injection of cholinesterase inhibitor-neostigmine. This study was designed to evaluate the role of interathecal neostigmine on local back pain relief after single level lumbar disc surgery.

Methods and Materials: In an interventional-expremental study (Imam Khomeini Hospital, Jun. 2000 to sep. 2001), sixty-six patient with unilateral herniated lumbr disc at one lumber space were randomely allocated into two groups including, control (C) group and Neostigmine (N) group. Both groups underwent fenestration employing same anesthetic techniques. At the end of surgery 2 ml normal saline in groups C and 100 micrograms neostigmine methylsulfate (0.2 ml combined with 1.8 ml normal saline) in group N were injected intrathecally postoperative local back pain was measured with 10 cm chart method using Visual Analogue Scale (VAS) at 1, 4, 8 and 12 hours. Total dosage of morphine, as an analgesic rescue, used during the first 24 hours following surgery and observed complications were recorded.

Results: Mean VAS score postoperatively at 1st and 4th hours were 2.24 (Standard Error Mean, SEM=0.36) and 1.82 (SEM=0.28) in group N and 5.36 (SEM=0.39) and 5.61 (SEM=0.37) in group C respectively. Mean morphine used in the first 24 hours was 0.9 (SEM=0.4) in group N and 4.7 (SEM=0.65) mg in group C. All result were found to be statistically different in the two group (P<0.05). There was no neurologic deficit or CSF leakage in both groups postoperatively. Regarding nausea and vomiting, the difference between two groups C (15 percent) and N (24.2 percent) were not significant statistically.

Conclusion: In this study, we have found that injection of 100 micrograms hyperbaric neostigmine intrathecally is a safe and effective method with minimal complications or side effect for pain relief and curtails postoperative opiate demand.