[Adjuvant methadone or fentanyl in spinal anesthesia with bupivacaine: a randomized, double-blind, placebo-controlled trial].

Objective: To compare the effect of combining spinal bupivacaine with either of 2 lipophilic opioids (fentanyl or methadone), testing the hypothesis that methadone would give longer-lasting analgesia.

Methods: Randomized, double-blind, placebo-controlled trial enrolling 69 women undergoing vaginal hysterectomy under spinal anesthesia (13 mg of 0.5% bupivacaine). The patients were randomized to 3 groups for use of different adjuvants: normal saline (placebo), 15 μg [DOSAGE ERROR CORRECTED] of fentanyl, or 3 mg of methadone. The main outcome was duration of analgesic effect measured as time elapsing until need for the first analgesic dose. The characteristics of the spinal blocks and adverse events were secondary outcome variables.

Results: Methadone significantly prolonged the duration of analgesia in comparison with the other adjuvants; with methadone, the effect was 1.9 times longer than in the placebo group and 1.5 times longer than in the fentanyl group. Duration of the sensory-motor block was significantly shorter in the methadone group (mean difference, 30 minutes). No differences in the incidences of adverse events were observed between the 2 opioid groups. No signs or symptoms suggestive of direct neurologic toxic effects were observed.

Conclusions: The addition of methadone to bupivacaine significantly prolonged the postoperative analgesic effect of spinal anesthesia and shortened sensory-motor block duration, enhancing patient comfort after surgery.