Indomethacin and the Preterm Infant with a Patent Ductus arteriosus: Relationship between Plasma Concentration and Ductus Closure

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Abstract
The relationship of indomethacin pharmacokinetics to clinical and échocardiographie evidence of closure of the patent ductus arteriosus (PDA) is described in 9 preterm infants. PDA closures occurred in 4 infants when peak indomethacin plasma concentrations were 0.71-1.10 pg/ml, mean 0.93 ±0.16 pg/ml. With partial or no PDA response to oral treatment, the peak concentrations were 0.20-0.69 pg/ml, mean 0.57 ± 0.08 pg/ml, p < 0.01. The left atrial size in the study infants correlated inversely with the indomethacin peak concentrations, r = 0.75. The plasma apparent terminal half-life correlated with postnatal age, r = 0.75. All patients with peak concentrations > 0.50 pg/ml had transient oliguria. This study suggests that a minimum indomethacin concentration may be needed to promote PDA constriction.