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Interaction between epidural 2-chloroprocaine and morphine: A randomized controlled trial of the effect of drug administration timing on the efficacy of morphine analgesia
Abstract Number: 248
Abstract Type: Original Research
Background: The efficacy and duration of epidural morphine analgesia is diminished when administered after 2-chloroprocaine compared to lidocaine. The mechanism of the interaction between 2-chloroprocaine (2-CP) and morphine is unknown. We hypothesized that administration of epidural morphine 30 min prior to the initiation of 2-CP anesthesia would result in postoperative analgesia of similar duration and quality to that achieved by administering epidural morphine after the initiation of lidocaine anesthesia in patients undergoing post-partum tubal ligation.
Methods: Subjects undergoing bilateral post-partum tubal ligation following vaginal delivery with epidural analgesia were randomized to one of three groups. Subjects received epidural morphine or saline 30 min prior to the initiation of analgesia with 3% 2-CP or 2% lidocaine, and at the time of surgical incision, they received either epidural saline or morphine. The duration of analgesia was defined as the time from morphine administration until the first request for supplemental analgesia. Duration of morphine analgesia was compared among groups using Kaplan-Meier survival analysis and the log-rank test.
Results: Administration of epidural morphine 30 min prior to the initiation of 2-CP (Group MCS, n=29) resulted in a longer median duration of analgesia (28.6 h [95% CI 4.4 to 52.7]) compared to morphine administered after 2-CP anesthesia (Group SCM, n=30) (2.2 h [95% CI 0 to 4.8]) (P=0.01). The median duration of analgesia in Group MCS was similar to that observed when morphine was administered after initiation of lidocaine anesthesia (Group SLM, n=28) (25.8 h [95% CI 10.7 to 40.9]) (P=0.95). Pain scores were not different in the post-anesthesia care unit, but were greater on admission to the postpartum unit in Group SCM. Supplemental morphine equivalents administered in the first 48 h were similar among groups and there were no differences in opioid-related side effects.
Discussion: This study demonstrates that administration of epidural morphine 30 min prior to epidural anesthesia with 2-CP provides a similar duration of analgesia as epidural morphine following epidural lidocaine anesthesia. This suggests that the observed interaction between epidural morphine and 2-CP is a result of differences in latency and duration of action of the two drugs, or that the administration of morphine before 2-CP effectively blocks a receptor site antagonism.