Dopamine pharmacokinetics in critically ill newborn infants.

Dopamine is frequently used in critically ill newborn infants for treatment of shock and cardiac failure, but its pharmacokinetics has not been evaluated using a specific analytical method. Steady-state arterial plasma concentrations of dopamine were measured in 11 seriously ill infants receiving dopamine infusion, 5-20 micrograms.kg-1.min-1, for presumed or proven sepsis and hypotensive shock. Steady-state concentrations of dopamine ranged from 0.013-0.3 microgram/ml. Total body clearance averaged 115 ml.kg-1.min-1. The apparent volume of distribution and elimination half life averaged 1.8 l.kg-1 and 6.9 min, respectively. No relationship was observed between dopamine pharmacokinetics and gestational age, postnatal age or birthweight. Substantial interindividual variation was seen in dopamine pharmacokinetics in seriously ill infants, and plasma concentrations could not be predicted accurately from its infusion rate. Marked variation in clearance explains in part, the wide dose requirements of dopamine needed to elicit clinical response in critically ill newborn infants.