Acetaminophen (paracetamol, N-(4-hydroxyphenyl) acetamide) is one of the
most commonly prescribed drugs for the management of pain in children.
Quantification of acetaminophen in pre-term and term neonates and small children
requires the availability of highly sensitive assays in small volume blood
samples.
We developed and validated an LC-MS/MS assay for the quantification of
acetaminophen in human plasma, cerebro-spinal fluid (CSF) and dried blood spots
(DBS). Reconstitution in water (DBS only) and addition of a protein
precipitation solution containing the deuterated internal standard were the only
manual steps. Extracted samples were analyzed on a Kinetex 2.6 μm PFP
column using an acetonitrile/formic acid gradient. The analytes were detected in
the positive multiple reaction mode. Alternatively, DBS were automatically
processed using direct desorption in a sample card and preparation (SCAP)
robotic autosampler in combination with online extraction.
The range of reliable response in plasma and CSF was 3.05-20,000 ng/ml
(r2 > 0.99) and 27.4-20,000 ng/ml (r2
> 0.99) for DBS (manual extraction and automated direct desorption).
Inter-day accuracy was always within 85-115% and inter-day precision for
plasma, CSF and manually extracted DBS were less than 15%. Deming
regression analysis comparing 167 matching pairs of plasma and DBS samples
showed a correlation coefficient of 0.98. Bland Altman analysis indicated a
26.6% positive bias in DBS, most likely reflecting the blood: plasma
distribution ratio of acetaminophen.
DBS are a valid matrix for acetaminophen pharmacokinetic studies.