Epidural administration of neostigmine and clonidine to induce labor analgesia: evaluation of efficacy and local anesthetic-sparing effect.

BACKGROUND Epidural clonidine produces analgesia without motor impairment, and is associated with a local anesthetic-sparing effect during labor. The authors have recently demonstrated that epidural neostigmine initiates selective labor analgesia devoid of adverse effects. Both drugs possess common analgesic mechanisms mediated through spinal acetylcholine release. This study evaluates their epidural combination in parturients. METHODS At the beginning of labor, parturients were randomly allocated to one of five groups to receive one of the following after a test dose: 150 microg epidural clonidine, 750 microg neostigmine, or 75 microg clonidine combined with 250, 500, or 750 microg neostigmine. A pain score (visual analog scale, 0-100) was recorded before administration and at regular intervals until request for a supplemental injection. Subsequent analgesia was provided by continuous epidural infusion of ropivacaine. RESULTS Parturients did not differ regarding demographic data and initial pain score. Clonidine 150 microg , neostigmine 750 microg , and 75 microg clonidine plus 250 microg neostigmine produced ineffective and short-lasting effects. Clonidine 75 microg plus 500 microg neostigmine and 75 microg clonidine plus 750 microg neostigmine presented comparable durations of 90 +/- 32 and 108 +/- 38 min (mean +/- SD), respectively, and final analgesic efficacies, with 72.2% and 84%, respectively, of the parturients reporting a visual analog scale score of less than 30 out of 100 after 30 min. Ropivacaine use was significantly reduced in all clonidine groups (average, 9.5 mg/h) in comparison with neostigmine alone (17 +/- 3 mg/h). No adverse effects were observed for 75 mug clonidine combined with any dose of neostigmine while maternal sedation (20%) and hypotension (33%) occurred with 150 microg clonidine alone. CONCLUSIONS Epidural clonidine, 75 microg , with 750 microg neostigmine is an effective combination to initiate selective labor analgesia without adverse effects. Clonidine use further reduces local anesthetic consumption throughout the course of labor.