Naloxone protein binding in adult and foetal plasma

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Abstract
Binding of naloxone hydrochloride was determined at 37°C, by equilibrium dialysis against 0.067 M phosphate buffer, pH 7.4, in plasma obtained from 18 healthy adults, and 18 samples of umbilical cord venous (foetal) plasma. The percentage free fraction (% free) in plasma was independent of naloxone concentration (9 ng/ml to 2.5 µg/ml). Percent free naloxone in adult (x=54.0) was lower (p1-acid glycoprotein (α1-AGP) and β-lipoprotein were higher (p1-AGP. It is suggested that qualitative differences in adult and foetal albumin and quantitative differences in plasma levels of α1-AGP and perhaps β-lipoprotein are responsible for naloxone plasma binding differences between adults and the newborn.