Clinical trial of naloxone in birth asphyxia.

To determine whether endogenous opiates play a role in the pathogenesis of perinatal asphyxia, a blinded clinical trial of naloxone, a competitive opiate receptor blocker, was undertaken in infants with low 1-minute Apgar scores. Of 85 infants with 1-minute Apgar score 0 to 3, 44 received an injection of naloxone (approximately 0.4 mg/kg) and 41 received saline solution. In 108 infants with 1-minute Apgar score 4 to 6, 54 received naloxone and 54 saline solution. In neither group was there a significant effect of naloxone on respiratory frequency or heart rate up to 30 minutes after injection, nor at 24 hours of age. In both groups active muscle tone of upper and lower limbs was increased by naloxone, a response that may not be beneficial in the face of inadequate oxygen delivery to vital organs. We conclude that naloxone at this dose had no readily apparent benefit in the resuscitation of the asphyxiated newborn infant.