Comparison of the antinociceptive effect of intrathecal versus intraperitoneal injection of paracetamol in neuropathic pain condition

Background: Despite the availability of several drug classes for treatment of neuropathic pain, no one provides the optimal balance of efficacy, tolerability and safety. Paracetamol (acetaminophen) is widely used for reducing pain with various origin around the world. The aim of this study was to compare the analgesic effect of intraperitoneally and intrathecally administration of paracetamol in chronic constriction Injury (CCI) model of the sciatic nerve in male rats.Method: In this study, ۲۴ adult male Wistar rats were randomly divided into ۲ groups (n=۱۲). The CCI model of sciatic nerve was used for induction of neuropathic pain. Catheterization was performed on the eleventh day after injury through the space between the L۵ and L۶. On the fourteen days after injury, paracetamol injected intraperitoneally (۱۰۰mg/kg) and intrathecally (۵۰μg / rat) in two different groups. Thermal and mechanical hyperalgesia and cold allodynia evaluated ۱۵, ۶۰ and ۱۲۰ minutes after injection. The intact limb was used as control.Results: Injury of the sciatic nerve induced a significant decrease in pain threshold. Both intraperitoneal (p<۰.۰۰۱) and intrathecal (p<۰.۰۰۱) administration of paracetamol reduced the pain and this effect continued until ۱۲۰ minutes after injection. However, paracetamol does not increase the pain threshold of injured hindpaw to the uninjured one. The effectiveness of paracetamol was similar in both methods of administration (p>۰.۰۵).Conclusion: The findings of this study indicate that intraperitoneal and intrathecal administration of paracetamol had no significant difference in pain symptoms. Therefore, because of convenience and lower risk, intraperitoneal administration is recommended to relief the pain.