[Clinical effects and pharmacokinetics of ropivacaine and bupivacaine for epidural analgesia during labor].

OBJECTIVE

To compare the analgesic efficacy, pharmacokinetics and histamine release of ropivacaine and bupivacaine with fentanyl in continuous epidural perfusion during labor and childbirth.

MATERIAL AND METHODS

Prospective study of 40 women at full-term pregnancy who requested epidural analgesia. The patients were randomly assigned to 2 groups of 20: group R received an initial bolus dose of 10 mL of 0.25% ropivacaine and group B received 0.25% bupivacaine, followed in both groups by epidural infusion of the assigned drugs at a concentration of 0.125% plus 0.30 mg of fentanyl at a rate of 5 mL/h through a patient-controlled analgesia device that allowed additional bolus doses. The studied variables were age, weight, height, sensory and motor block, mean blood pressure and maternal-fetal heart rates, number of bolus doses, total local anesthetic administered, duration and type of delivery, oxytocin increase, Apgar at 1 and 5 minutes, plasma levels of local anesthetic (30 minutes after the initial dose, at the end of dilation, in the umbilical vein, and 30 minutes after switching off the perfusion pump), time to clearance, elimination half-life, and a test of histamine release by radioimmunoassay.

RESULTS

No significant differences were observed in the course of labor or in Apgar scores. The plasma concentrations of ropivacaine were higher than those of bupivacaine (p<0.03). Clearance of both drugs was similar. The elimination half-life of ropivacaine was significantly less than that of bupivacaine (5.2 +/- 0.7 h vs. 10.8 +/- 1.06 h).

CONCLUSIONS

Analgesia was equally effective in both groups, without adverse maternal-fetal effects, with spontaneous micturition and absence of motor blockade in both groups. The plasma concentrations were higher with ropivacaine but were not toxic.