Obstetric analgesia: pharmacokinetics and its relation to neonatal behavioral and adaptive functions.

The neonatal pharmacokinetic and neurobehavioral properties of certain agents used in obstetric analgesia are reviewed (local anesthetics, opiates, inhalation agents, benzodiazepines). Fetal and neonatal pharmacokinetic alterations partly explain the neurobehavioral differences observed between different drug groups and ways of drug administration. The most effective and safest method with fewest neonatal neurobehavioral effects appears to be regional epidural analgesia performed with plain bupivacaine. The use of epidural opiates remains problematic. Inhalation agents and parenteral pethidine (meperidine) are still clinically useful alternative compounds in circumstances where epidural analgesia is not possible. Pharmacokinetically and according to neurobehavioral assessments, inhalation agents appear to be more attractive than pethidine. Benzodiazepines, especially after high or repeated doses, may cause the so-called floppy-infant syndrome, at least partly, due to a slow neonatal drug elimination.