Systemic opioids are commonly administered during labor, but their efficacy has been recently questioned. In addition, laboratory and clinical studies provide a strong rationale for combining mu- and kappa-opioid receptor agonists for analgesia. The authors therefore studied, using validated intensity and affective scales and definitions of effective pain relief, the efficacy of intravenous meperidine, butorphanol, and their combination for labor analgesia. Healthy women with singleton term pregnancy requesting analgesia during active labor were studied. Women were randomly assigned to receive 50 mg meperidine, 1 mg butorphanol, or 25 mg meperidine plus 0.5 mg butorphanol (n = 15/group). Pain intensity was assessed using a 0-10 numerical rating scale, and affective magnitude was assessed using a ratiometric descriptive scale before drug administration and between the sixth and seventh uterine contractions after drug administration. All three treatments reduced pain intensity equally. Butorphanol alone did not reduce pain affective magnitude, whereas the other treatments did. There was a significant correlation between reduction in pain intensity and affective magnitude in all groups, with greater reductions in affective magnitude than intensity. Overall, 29% of women exhibited clinically meaningful pain relief, with no difference among groups. Groups did not differ in incidence of opioid-induced adverse effects. These doses of meperidine and butorphanol do reduce pain intensity and affective magnitude, although a minority of patients achieve meaningful pain relief as defined in multiple patient populations, including laboring women. Combination of these drugs did not improve their therapeutic benefit.
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Jan 1, 2006
D.H Chestnut 
Open Access