A tandem mass spectrometry assay for the simultaneous determination of acetaminophen, caffeine, phenytoin, ranitidine, and theophylline in small volume pediatric plasma specimens

Background: Acetaminophen. caffeine, phenytoin, ranitidine, and theophylline are widely used in pediatric pharmacotherapy, but only very limited information is available on the pharmacokinetics of these medications in premature neonates. As pharmacokinetic studies in this population are hampered by limitations in the number and volume of plasma samples, we developed an LC-MS/MS assay for the simultaneous determination of these medications in small volume human plasma specimens for pharmacokinetic evaluations in neonates. Methods: Sample preparation was performed by protein precipitation with methanol after addition of internal standard to 50 mu l of plasma specimen. After chromatographic separation on a C18 column using gradient elution, analytes were detected using a triple quadrupole mass spectrometer that was operated in positive ion mode with electrospray ionization. Results: All 5 analytes could be simultaneously quantified in human plasma. The linear quantification range comprised 12.2 to 25,000 ng/ml for acetaminophen, phenytoin, and ranitidine, 24.4 to 25,000 ng/ml for theophylline. and 48.8 to 25,000 ng/ml for caffeine with accuracies ranging from 87.5 to 115.0%. The intra-day and inter-day precision (%CV) was between 2.8 and 11.8% and 4.5 and 13.5%, respectively. Conclusions: An accurate, sensitive, and reliable LC-MS/MS method was developed and validated to simultaneously quantify 5 drugs frequently used in neonatal pharmacotherapy. (C) 2008 Elsevier B.V. All rights reserved.