Effects of age on the serum concentration of α 1 ‐acid glycoprotein and the binding of lidocaine in pediatric patients

We determined the effect of age on the serum concentration of α 1 ‐acid glycoprotein (α 1 ‐AGP) in venous blood from 134 subjects who ranged in age from preterm neonates to 18‐year‐old adolescents. The mean (± SD) serum concentration of α 1 ‐AGP, determined by radial immunodiffusion, increased significantly with age: the concentration found in neonates was less than that found in infants which, in turn, was less than that found in older children ( p < 0.001). In addition, we determined the effect of α 1 ‐AGP on the free fraction of lidocaine in four groups of infants and children who received intravenous lidocaine (1.5 mg/kg). The percentage of free lidocaine correlated inversely and linearly with the serum α 1 ‐AGP concentration (r 2 = 0.617; p < 0.001). The percentage of free lidocaine in the five neonates exceeded that in the older age groups. We conclude that the serum concentration of α 1 ‐AGP increases while the free fraction of lidocaine decreases from early infancy to adolescence. Clinical Pharmacology and Therapeutics (1989) 46 , 219–225; doi: 10.1038/clpt.1989.129