Dose-response study of intrathecal morphine versus intrathecal neostigmine, their combination, or placebo for postoperative analgesia in patients undergoing anterior and posterior vaginoplasty

This study was designed to examine postoperative analgesia with intrathecal neostigmine in a randomized, blinded trial with morphine as the active control in patients undergoing anterior and posterior vaginoplasty. A secondary aim was to provide preliminary data on the interaction between these two drugs. The incidence of adverse effects was also assessed. Forty-eight patients were divided into eight groups (50 mu g, 100 mu g, and 200 mu g morphine [M]; saline; 50 mu g, 100 mu g, and 200 mu g neostigmine [N]; and 50 mu g morphine + 50 mu g neostigmine). Anesthesia was provided with a balanced technique. All patients stayed 24 h in the recovery room where adequacy of postoperative analgesia and side effects were assessed. increasing doses of intrathecal morphine (50 mu g, 100 mu g, and 200 mu g) and intrathecal neostigmine (50 mu g, 100 mu g, and 200 mu g) showed a dose-dependent pattern of analgesia (P < 0.001). The M50 + N50 combination resulted in a better analgesic effect with fewer side effects than M50, N50, and control groups. These preliminary data suggest that spinal neostigmine produces analgesia for vaginoplasty surgery similar in duration to spinal morphine and that the combination of morphine and neostigmine may allow a reduction in the dose of each component for postoperative analgesia.