A double-blind comparison of intramuscular pethidine and nalbuphine in labour

A double-blind, between-patient comparison of intramuscular pethidine 100 mg and nalbuphine 20 mg for the relief of pain during labour in 80 patients is described. Severity of pain was assessed before and after treatment by subjective pain scores and visual analogue scales. Neither of these methods showed a significant difference between the treatments. Nalbuphine was associated with less maternal nausea and vomiting than pethidine, but this possible advantage was somewhat offset by a tendency of the drug to produce more maternal sedation and dizziness. The mean umbilical vein/maternal vein ratio was significantly higher for nalbuphine (0.78, SEM 0.03) than for pethidine (0.61, SEM 0.02), which suggests easier placental transfer of the former. This finding was reflected in significantly lower 2-4 hour neurobehavioural scores for the infants of mothers given nalbuphine, but there was no significant difference between these scores at 24 hours. On the basis of this study, nalbuphine does not offer a substantial improvement over pethidine for pain relief in labour.