A simple rapid and sensitive HPLC technique for the analysis of total and free plasma indomethacin concentrations in neonates is described. The advantages of the technique are small sample volumes (50 μL) enabling the use of capillary samples, direct extraction, low limits of detection (20 ng/mL) and good precision (CV<7% between-batch). Indomethacin and the internal standard (flufenamic acid) eluted within 12 min and the peaks were unaffected by indomethacin metabolites or by a number of commonly used drugs. The technique is suitable for the investigation into the pharmacokinetics of total and free indomethacin, in neonates with patent ductus arteriosis, and could be used to define a therapeutic window for free indomethacin levels to enable therapeutic drug monitoring to occur in this condition.
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