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Substantial Differences in Serum Concentrations of Psychoactive Drugs Measured in Samples Stored for 2 Days or More on Standard Serum Tubes Versus Serum Tubes Containing Gel Separators

Wollmann, Birgit M., MSc*; Lunde, Hilde A., MA*; Støten, Lene K., MSc*; Lunder, Niclas, MSc*; Molden, Espen, PhD*,†

doi: 10.1097/FTD.0000000000000592
Short Communication

Background: Drugs may potentially adsorb to blood collection tubes containing gel separators in the preanalytical phase of therapeutic drug monitoring. The aim of this study was to compare measured concentrations of 28 psychoactive drugs and 13 metabolites in spiked serum samples stored on standard (plain) tubes versus barrier gel tubes during a 2–6-day period at room temperature.

Methods: Drug-free (“blank”) serum samples spiked with mixes of antidepressants, antipsychotics, or mood stabilizers (valproic acid and lamotrigine), including relevant metabolites, were transferred to tubes with and without gel, that is, BD Vacutainer SST II Advance gel tubes and BD Vacutainer Glass Serum Tubes (Becton-Dickinson Company, Plymouth, United Kingdom). Mean serum concentrations of the drugs or metabolites measured by ultra-high performance liquid chromatography–tandem mass spectrometry analyses of protein-precipitated samples were compared after storage on plain or gel tubes at 3 time points (day 0, day 2/48 hours, and day 6/144 hours) in room temperature.

Results: Mean serum concentrations of all antidepressants, except for one metabolite, and 13 of 18 antipsychotic drugs were significantly lower in gel tubes compared with plain tubes after 2 days of storage (2%–28% lower, P < 0.05). After 6 days of storage, mean serum concentrations of all antipsychotic drugs and antidepressants were significantly lower in gel tubes versus plain tubes (9%–49% lower, P < 0.02), except for amisulpride and O-desmethylvenlafaxine. Serum concentrations of the mood stabilizers were not significantly different in gel tubes compared with plain tubes (P > 0.1). There was a clear relationship between log P (partition coefficient) and residual serum concentrations during gel tube storage (r −0.50 and −0.42 at day 2 and day 6, respectively; P < 0.02).

Conclusions: This study shows that storage on gel for more than 2 days significantly decreases the serum concentrations of antidepressant and antipsychotic drugs as compared to storage in plain tubes. Thus, using tubes with gel separators in the therapeutic drug monitoring of psychoactive drugs should be reconsidered.

*Center for Psychopharmacology, Diakonhjemmet Hospital; and

Department of Pharmaceutical Biosciences, School of Pharmacy, University of Oslo, Oslo, Norway.

Correspondence: Birgit M. Wollmann, MSc, Center for Psychopharmacology, Diakonhjemmet Hospital, PO Box 23, Vinderen, N-0319, Oslo, Norway (e-mail:

H. A. Lunde and B. M. Wollmann contributed equally to this work and share the first authorship.

The authors declare no conflict of interest.

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Received August 02, 2018

Accepted November 01, 2018

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