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24 Clinical validation study to derive conversion factors from capillary blood concentration to plasma concentration for venlafaxine and desvenlafaxine
Introduction In the last years, several new products to enable TDM with capillary blood entered the market. To interpret capillary blood concentrations with current therapeutic reference ranges, conversion factors have to be established with clinical validation studies.
Methods A study for venlafaxine and desvenlafaxine has been conducted with volumetric absorptive microsampling (VAMS) as sampling device in two hospitals in Münster (Germany) with 49 patient samples over a period of one year. After giving written informed consent, blood out of the vein and an additional drop of blood out of the fingertip was drawn and analyzed by LC-MS. The obtained data was analyzed with Passing-Bablok regression and Bland-Altman analysis.
Results A good correlation between capillary blood and plasma concentrations could be achieved with a pearson’s R above 0.93 and a conversion factor of 0.87 for venlafaxine and 0.75 for desvenlafaxine. The conversion factors passed the cross-validation test according to EMA guidelines with Bland-Altman analysis.
Conclusion After one year, 49 patient samples could be collected and analyzed. The resulting Passing-Bablok regressions and Bland-Altman analysis led to conversion factors, which are suitable for the application in routine healthcare. The established method can now be used to offer TDM to an ambulant setting by patient self-sampling or sampling in pharmacies or through nurses. This enables the opportunity of a faster, easier and more widespread use of TDM.
30 April 2020 (online)
© Georg Thieme Verlag KG
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