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 and safety of intrathecal neostigmine for the relief of pain for patients having undergone inguinal herniorrhaphy surgery.
Methods: Sixty men scheduled for elective inguinal herniorrhaphy with spinal anaesthesia were randomly allocated to three groups: group I (n=20) received intrathecal (IT) tetracaine 15 mg, group II (n=20) received IT tetracaine 15 mg+ neostigmine 50 microg, and group III (n=20) received IT tetracaine 15 mg+neostigmine 100 microg. 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 administration.
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 prolonged for group III patients, with 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 group II patients. There was a significantly greater incidence of adverse effects associated with IT neostigmine, especially nausea and vomiting.
Conclusion: Our study showed that intrathecal neostigmine at 50 pg or 100 microg enhanced the onset of tetracaine anaesthesia and provided analgesia lasting for 6-9 h, although increased incidences of prolonged motor blockade and nausea or vomiting were noted.