Prophylactic oral naltrexone with intrathecal morphine for cesarean section: effects on adverse reactions and analgesia

The influence of two different doses of oral naltrexone on the adverse effects and the analgesia associated with intrathecal morphine was compared in a double-blind, placebo-controlled study. Thirty-five patients undergoing cesarean section were provided postoperative analgesia by 0.25 mg intrathecal morphine. Sixty minutes later they were given 6 mg naltrexone, 3 mg naltrexone, or placebo as an oral solution. Pain relief was assessed by the Visual Analog Scale. Requirements for additional analgesics and side effects were recorded. Duration of analgesia was shorter in the 3- and 6-mg naltrexone groups than in the placebo group, 10.0 +/- 2.6, 12.4 +/- 2.6, and 19.2 +/- 4.5 h (mean +/- SEM), respectively, but values did not reach statistical significance. The incidence of pruritus and vomiting was significantly less in the 6-mg naltrexone group than in the other two groups (P less than 0.05). Somnolence was significantly less in the 3- and 6-mg naltrexone groups than in the placebo group (P less than 0.05). Naltrexone (6 mg) is an effective oral prophylactic against the pruritus and vomiting associated with intrathecal morphine for analgesia after cesarean section, but it is associated with shorter duration of analgesia.