Acetaminophen serum concentrations in infants treated intravenously for patent ductus arteriosus

OBJECTIVE Although acetaminophen has emerged as a therapeutic option for treating hemodynamically significant patent ductus arteriosus (PDA) in preterm infants, limited data exist on pharmacodynamics. The objective of this research is to report serum acetaminophen concentrations at steady state in infants treated with intravenous acetaminophen for PDA and to examine associations with clinical outcomes. METHODS This retrospective study evaluated all infants admitted during the study period who received intravenous acetaminophen for the treatment of PDA. Acetaminophen dosing was 15 mg/kg every 6 hours. A serum acetaminophen concentration was obtained 4 hours after the eighth dose. Associations between serum concentrations and efficacy, assessed by ductal constriction on echocardiogram, and safety, assessed by serum creatinine and hepatic transaminases, were explored using simple linear regression. RESULTS A total of 36 infants were included, with a median birth weight of 720 g (IQR 585–895 g) and a median gestational age of 25 weeks (IQR 24–26 weeks). The median acetaminophen concentration in the cohort was 12.3 mg/L (IQR 6.7–16.5 mg/L; range, 1.1–29.0 mg/L). Serum acetaminophen concentrations did not correlate with infant demographics, hepatic transaminases during treatment, or duct size at treatment completion. We observed ductal closure across a wide range of serum acetaminophen concentrations. CONCLUSIONS We did not identify an association between acetaminophen serum concentrations following intravenous therapy and ductal response or hepatic toxicity.