Obstetric analgesia and infant outcome in monkeys. Neonatal measures after intrapartum exposure to meperidine or alfentanil.

Neurobehavioral evaluations were conducted in neonatal monkeys (Macaca mulatta) exposed to narcotic analgesics during labor through their dams. Infants exposed to meperidine (2 mg/kg maternal dose) or alfentanil (0.1 mg/kg maternal dose) were compared with controls whose dams received no analgesic. Meperidine and alfentanil differ in pharmacologic properties related to maternal-fetal transfer and neonatal metabolism. Drug-exposed infants showed neurobehavioral effects over the first 3 days of life including depressed respiration (at birth), depressed environmental response to aversive stimuli (days 0, 1, and 2), more overnight sleep (day 1), and more quiet behavior patterns while awake (day 3). In addition, drug exposure was associated with increased elicited muscle tone early in the neonatal period and earlier maturation of sitting, standing, and walking. No effects on growth or health were noted, but drug-exposed infants had lower hematocrits and an earlier onset of a linear growth rate as reflected in body weight. No qualitative or quantitative differences were noted between the two drug treatments. Because behavioral effects were seen after the drug was eliminated, a direct pharmacologic action of the drug does not fully explain the findings.