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Fast and sensitive LC-MS/MS assay for quantification of nortriptyline and its active metabolites E- and Z-10-hydroxynortriptyline in human plasma.

BACKGROUND
A fast and sensitive validated assay for nortriptyline, E-10-hydroxynortriptyline and Z-10-hydroxynortriptyline in plasma following a single oral dose of nortriptyline 25 mg was needed to support a clinical study.


RESULTS
Plasma samples were prepared by protein precipitation, separated on a C18 column with a mobile phase consisting of 0.1% formic acid in an acetonitrile gradient over 6 min and detected by ESI in the positive mode and MS/MS. Mean recoveries of at least 90% were achieved. The LLOQ was 0.2 ng/ml for nortriptyline and 0.5 ng/ml for the metabolites. The standard curve was linear within LLOQ to 40 ng/ml (r(2) ≥ 0.997), precision was under 7.1% coefficient of variance (<16% at LLOQ) and accuracy was 92-114%.


CONCLUSION
A fast and sensitive assay for nortriptyline, E- and Z-10-hydroxynortriptyline in plasma was developed and validated. It has been applied successfully to a clinical study.