An infant body plethysmograph and end-tidal CO, sampling were used to study respiratory CO, response curves in newborn male infants. CO, response curves were obtained before and after the administration of meperidine or morphine. In infants given one third the dose of each compound e8tablished to yield equivalent respiratory depression in the adult, morphine shifted the CO, response curve to the right and downward to a greater extent than meperidine. The greater susceptibility to morphine in the infant as compared to the adult is believed to be due primarily to a greater permeability of the infant brain to morphine.

No abstract