Atenolol elimination in the neonate.

The elimination of the cardioselective beta-adrenoceptor antagonist atenolol has been studied in 35 neonates by measuring drug concentration in cord blood and in blood obtained at 24 h by heel stab. Elimination rate was assessed by calculating the slopes of lines joining these two concentration points. The slopes had a mean of 0.043 h-1 (equivalent to a half-life of 16 h) and were normally distributed with 95% of values being in the range 0.02-0.066. There was no relationship between slope and neonatal weight or skinfold thickness, but most babies were at term and the range of these indices was narrow. Babies who developed a bradycardia had cord atenolol concentrations and slopes which did not differ significantly from those in babies without bradycardia. We conclude that atenolol elimination in the neonate is reduced when compared to adults. This prolonged elimination is consistent with the physiological characteristics of this age group and with previous observations on drugs eliminated by renal excretion.