Comparison of 0.25% S(-)-bupivacaine with 0.25% RS-bupivacaine for epidural analgesia in labour

We have compared the efficacy of 0.25% S(-)-bupivacaine with 0.25% RS-bupiv acaine in providing epidural analgesia for labour in a randomized, multicen tre, double-blind study. Analgesia was initiated with 10 ml of the study so lution and maintained with 10-ml top-ups. We studied 137 women and treatmen ts were found to be equivalent for onset. duration and quality of block Med ian onset of pain relief was 12 min for both drugs and median duration was 49 (range 3-129) min and 51 (7-157) min for S(-)-bupivacaine and RS bupivac aine, respectively. The estimated treatment difference for duration of pain relief was -4 (90% CI -13, 6) min. Thirty patients failed to achieve pain relief after the first injection (20 patients after S(-)-bupivacaine and 10 after RS-bupivacaine; P=0.039). However, median duration of pain relief fr om the first top-up was 82 (range 3-164) min for S(-)-bupivacaine and 76 (2 2-221) min for RS-bupivacaine. There were no significant differences in the quality of analgesia, as assessed by the investigators. There were no sign ificant differences in the extent of sensory block, percentage of patients with motor block or incidence of adverse events.