Efficacy of intrathecal neostigmine for the relief of postinguinal hemiorrhaphy pain

Background: Intrathecal administration of various doses of neostigmine has been reported to produce analgesia without neurotoxicity in both animal and human studies. The present study was undertaken to evaluate the efficacy a nd safety of intrathecal neostigmine for the relief of pain for patients ha ving undergone inguinal herniorrhaphy surgery. Methods: Sixty men scheduled for elective inguinal herniorrhaphy with spina l anaesthesia were randomly allocated to three groups: group I (n=20) recei ved intrathecal (IT) tetracaine 15 mg, group II (n=20) received IT tetracai ne 15 mg+ neostigmine 50 mu g, and group III (n=20) received IT tetracaine 15 mg+neostigmine 100 mu g. The onset of anaesthesia, duration of analgesia , time to use of first rescue analgesics, the overall 24-h VAS pain scores and the incidence of adverse effects were recorded for 24 h postdrug admini stration. Results: Onset of anaesthesia (time to T6 sensory block) was significantly faster for group II and III patients compared with group I patients. Motor block (time to lift leg) was greatly pro longed for group III patients, wit h an average of 6.4 h, compared with 4.1 h for group II patients. Group III patients also showed a later onset of postsurgical pain, lower overall 24- h VAS pain score and prolonged time to first rescue analgesics than did gro up II patients. There was a significantly greater incidence of adverse effe cts associated with IT neostigmine, especially nausea and vomiting. Conclusion: Our study showed that intrathecal neostigmine at 50 mu g or 100 mu g enhanced the onset of tetracaine anaesthesia and provided analgesia l asting for 6-9 h, although increased incidences of prolonged motor blockade and nausea or vomiting were noted.