Analgesic effects of intrathecal neostigmine.

EDITOR: We read about the analgesic effects of intrathecal neostigmine in perianal surgery by Yegin and colleagues with great interest [1]. We agree with them, as we found very similar results, that intrathecal neostigmine increases sensory blockade, motor blockade and increases the incidence of adverse effects such as nausea and vomiting. Hood and colleagues in 1995 suggested that intrathecal neostigmine causes increase in analgesia, motor weakness, decrease in deep tendon reflexes, urinary retention, nausea and vomiting in a dose-dependent manner [2]. Lauretti and colleagues in 1996 conducted a study in human beings to evaluate the analgesic action of intrathecal neostigmine quantitatively and showed that neostigmine 100 μg gave better analgesia for somatic pain than visceral pain [3]. We tested the efficacy of intrathecally administered neostigmine methylsulphate for intraoperative and postoperative analgesia, in patients undergoing orthopaedic surgery of the lower limbs. Sixty ASA I–II adult patients were enrolled. The Medical Ethics Committee of Seth G. S. Medical College and King Edward Memorial Hospital, Mumbai, India, approved the study protocol, and written informed consent was obtained from each patient. They were randomly divided into two equal groups. Group A received hyperbaric bupivacaine 0.5% 15 mg (3 mL) plus dextrose 5% (0.5 mL). Group B received hyperbaric bupivacaine 0.5% 15 mg (3 mL) with neostigmine 250 μg (0.5 mL). Neostigmine prolonged the sensory and motor blockade produced by bupivacaine. The mean duration of sensory blockade was: Group A, 174.50 27.65 min; Group B, 309 62.64 min (P 0.001). The mean duration of motor block was: Group A, 158.67 25.80 min; Group B, 221 34.37 min (P 0.001). The mean duration of postoperative analgesia in Group B was 706.66 175.20 min compared to 60.33 45.44 min in Group A. This data suggests that intrathecal neostigmine produces prolonged postoperative analgesia. Nineteen patients of our study group developed nausea and vomiting; all responded to intravenous (i.v.) ondansetron. Our findings clearly show that intrathecal neostigmine prolongs postoperative analgesia but not without prolonging the motor blockade and causing nausea and vomiting. So in view of the motor blockade and excessive nausea and vomiting caused by intrathecal neostigmine 250 μg, we are unable to recommend its use as a spinal anaesthetic.