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Zopiclone degradation in biological samples: Characteristics and consequences in forensic toxicology
Linköping University, Department of Medical and Health Sciences, Division of Drug Research. Linköping University, Faculty of Health Sciences.
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Bio-analytical results are influenced by in vivo factors such as genetics, pharmacological and physiological conditions and in vitro factors such as specimen composition, sample additives and storage conditions. Zopiclone (ZOP) is a short-acting hypnotic drug (Imovane®) used for treatment of insomnia. ZOP is metabolized by three major pathways; oxidation to the active zopiclone N-oxide (ZOPNO), demethylation to the inactive N-desmethylzopiclone (NDZOP) and oxidative decarboxylation to other inactive metabolites. ZOP is increasingly being encountered in forensic cases and is a common finding in samples from drug-impaired drivers, users of illicit recreational drugs, victims of drug facilitated sexual assaults and forensic autopsy cases. ZOP is a notoriously unstable analyte in biological matrices and analytical results depend on pre-analytical factors, such as storage time and temperature. The overall aim of this thesis was to investigate the stability of ZOP and the factors of importance for degradation during storage in biological samples and to identify consequences for interpretation of results in forensic toxicology.

In paper I, different stability tests in spiked samples were performed including short-term, longterm, freeze-thaw and processed stability. Analyses of ZOP were performed by gas chromatography with nitrogen phosphorous detection and ZOP concentrations were measured at selected time intervals. The degradation product 2-amino-5-chloropyridine (ACP) was identified using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The stability investigations showed a very poor short-term storage stability of ZOP.

Therefore, in paper II, the influence of pre-analytical conditions was further investigated in dosed subjects. Whole blood from volunteers was obtained before and after oral administration of Imovane®. In this study, the influence from physiological factors such as drug interactions, matrix composition and plasma protein levels were minimized. The results showed that ZOP was stable in whole blood for only one day at room temperature, one week in a refrigerator and at least three months frozen in authentic as well as in spiked whole blood. The rapid degradation of ZOP at ambient temperature can cause an underestimation of the true concentration and consequently flaw the interpretation. However, by also analyzing the degradation product ACP the original concentration of ZOP may be estimated.

In papers III and IV, two LC-MS-MS methods were validated for the quantitation of ACP, ZOP and NDZOP in blood and ACP, ZOP, NDZOP and ZOPNO in urine. These methods were used in a controlled pharmacokinetic study where whole blood and urine were obtained after oral administration of Imovane®. Samples of blood and urine were aliquoted, analyzed and stored under different conditions and the formation of ACP was monitored. Additionally, at each studied time point the pH of the blood and urine samples was measured using i-STAT® system. The results showed that ACP was formed in equimolar amounts to the degradation of ZOP and its metabolites.

In urine samples, the formation of ACP occurred at elevated pH or temperature and mirrored the degradation of ZOP, NDZOP and ZOPNO. The high concentrations of metabolites, which also degraded to ACP, made it impossible to estimate the original ZOP concentration.

The results from analysis of blood samples containing ACP were also used to develop mathematical models to estimate the original ZOP concentration. Both models showed strong correlation to the original ZOP concentration (r=0.960 and r=0.955) with p<0.01. This study showed that the equimolar degradation of ZOP and NDZOP to ACP could be used to estimate the original concentration of ZOP in blood samples.

Absence of ACP in the blood or urine samples analysed strongly suggests that degradation has not occurred and that the measured concentration of ZOP is reliable. For proper interpretation in forensic cases, it is strongly recommended that ZOP and its metabolites as well as ACP are included in the analysis.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014. , 68 p.
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1395
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:liu:diva-105821DOI: 10.3384/diss.diva-105821ISBN: 978-91-7519-397-7 (print)OAI: oai:DiVA.org:liu-105821DiVA: diva2:710932
Public defence
2014-04-24, Eken, Hälsouniversitetet, Campus US, Linköpings universitet, Linköping, 13:00 (Swedish)
Opponent
Supervisors
Available from: 2014-04-08 Created: 2014-04-08 Last updated: 2014-04-08Bibliographically approved
List of papers
1. Stability tests of zopiclone in whole blood
Open this publication in new window or tab >>Stability tests of zopiclone in whole blood
2010 (English)In: Forensic Science International, ISSN 0379-0738, E-ISSN 1872-6283, Vol. 200, no 01-Mar, 130-135 p.Article in journal (Refereed) Published
Abstract [en]

Zopiclone is a common drug in forensic cases and it is frequently analyzed in biological materials using different analytical methods. Zopiclone is unstable in certain solvents and depending on storage conditions unstable in biological fluids; however its stability in human whole blood has not yet been established in detail. Therefore, the following investigation was performed to study the stability of zopiclone in both spiked and authentic human blood. First, spiked blood samples were stored at -20 degrees C, 5 degrees C and 20 degrees C and the degradation of zopiclone was investigated. Second, authentic and spiked blood samples were stored at 5 degrees C and differences in zopiclone stability were studied. Third, processed sample stability and effect of freeze/thaw cycles were evaluated. Analyses were performed by GC-NPD and zopiclone concentrations were measured at selected time intervals. The study showed that zopiclone degrades in human blood depending on time and temperature and may not be detected after long-term storage. 2-amino-5-chloropyridine was identified as the primary degradation product from zopiclone. At refrigerator temperature zopiclone was stable less than 1 month in both spiked and authentic human blood samples. The best storage condition was at -20 degrees C even at short storage times, as freeze-thaw had no influence on the results. In butyl acetate extracts, zopiclone was stable at least 2 days when kept in the autosampler at ambient temperature. We conclude that preanalytical factors have great impact on analytical results and should be addressed when interpreting whole blood zopiclone concentrations.

Place, publisher, year, edition, pages
Elsevier Science B.V., Amsterdam., 2010
Keyword
Degradation; Forensic toxicology; Stability; Storage; Zopiclone
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-58328 (URN)10.1016/j.forsciint.2010.04.001 (DOI)000279024800017 ()
Available from: 2010-08-13 Created: 2010-08-11 Last updated: 2017-12-12Bibliographically approved
2. Influence of pre-analytical conditions on the interpretation of zopiclone concentrations in whole blood
Open this publication in new window or tab >>Influence of pre-analytical conditions on the interpretation of zopiclone concentrations in whole blood
2011 (English)In: Forensic Science International, ISSN 0379-0738, E-ISSN 1872-6283, Vol. 207, no 1-3, 35-39 p.Article in journal (Refereed) Published
Abstract [en]

Zopiclone is a short-acting hypnotic drug used for treatment of insomnia and its stability has been described in some detail. However, data especially on short-term pre-analytical stability is missing. This study investigated zopiclone stability differences between spiked and authentic whole blood from subjects dosed with zopiclone. In this way influence from physiological factors such as drug interactions, matrix composition and plasma protein levels were minimized. Nine volunteers participated in the study. Whole blood was obtained before and after oral administration of 10 mg Imovane®. Aliquots of 1 g of authentic and spiked blood were after initial measuring, stored at 20°C during 5 days, 5°C or -20°C during 3 months, and zopiclone was measured by gas chromatography with nitrogen phosphorus detection. The results showed no stability differences between authentic and spiked blood but confirmed the very short stability in whole blood at ambient temperature. In summary, the stability was less than 1 day at 20°C, less than 2 weeks at 5°C, but stable for 3 months at -20°C. This study demonstrates the importance of controlling pre-analytical conditions from sampling to analysis to avoid misinterpretation of toxicological results.

Place, publisher, year, edition, pages
Elsevier, 2011
Keyword
Degradation; Forensic toxicology; Stability; Storage; Zopiclone
National Category
Pharmacology and Toxicology
Identifiers
urn:nbn:se:liu:diva-59046 (URN)10.1016/j.forsciint.2010.08.016 (DOI)000288851300028 ()20851542 (PubMedID)
Available from: 2010-09-07 Created: 2010-09-07 Last updated: 2017-12-12Bibliographically approved
3. Quantitative Analysis of Zopiclone, N-desmethylzopiclone, Zopiclone N-oxide and 2-Amino-5-chloropyridine in Urine Using LC-MS-MS
Open this publication in new window or tab >>Quantitative Analysis of Zopiclone, N-desmethylzopiclone, Zopiclone N-oxide and 2-Amino-5-chloropyridine in Urine Using LC-MS-MS
2014 (English)In: Journal of Analytical Toxicology, ISSN 0146-4760, E-ISSN 1945-2403, Vol. 38, no 6, 327-334 p.Article in journal (Refereed) Published
Abstract [en]

A simple LC-MS/MS method was validated to allow determination of zopiclone (ZOP), Ndesmethylzopiclone (NDZOP), zopiclone N-oxide (ZOPNO) and 2-amino-5 chloropyridine (ACP) in urine at concentrations up to 3000 ng/mL within 3.5 min. This method was used for quantitative analysis of the analytes in authentic urine samples obtained 10 h after oral administration of zopiclone (Imovane®) and in aliquots of the same urine samples after different storage conditions. Additionally, pH of each studied urine sample was measured over time. The results showed that formation of ACP occurred at elevated pH and/or temperature by degradation of ZOP, NDZOP and ZOPNO. This method was also applied to samples obtained from two female victims of drug-facilitated assault. One sample had been exposed to long-term storage conditions at different temperatures and at pH>8.2, which resulted in high concentrations of ACP. The other sample, which was exposed to pH <6.5, showed no formation of ACP. ACP is formed both from ZOP and from its metabolites NDZOP and ZOPNO depending on the pH of the urine, time of storage and/or the temperature conditions. For correct interpretation in forensic cases ZOP, its major metabolites and ACP should be analyzed. When ACP is identified in urine the concentrations of ZOP, NDZOP and ZOPNO should be interpreted with great caution.

Place, publisher, year, edition, pages
Oxford University Press (OUP): Policy F, 2014
Keyword
Degradation; Forensic toxicology; Zopiclone; LC-MS-MS
National Category
Clinical Medicine Pharmacology and Toxicology
Identifiers
urn:nbn:se:liu:diva-105819 (URN)10.1093/jat/bku042 (DOI)000340069000004 ()
Available from: 2014-04-08 Created: 2014-04-08 Last updated: 2017-12-05Bibliographically approved
4. Validation of an LC-MS/MS method for the determination of zopiclone, N-desmethylzopiclone and 2-amino-5-chloropyridine in whole blood and its application to estimate the original zopiclone concentration in stored specimens
Open this publication in new window or tab >>Validation of an LC-MS/MS method for the determination of zopiclone, N-desmethylzopiclone and 2-amino-5-chloropyridine in whole blood and its application to estimate the original zopiclone concentration in stored specimens
2015 (English)In: International journal of legal medicine (Print), ISSN 0937-9827, E-ISSN 1437-1596, Vol. 129, no 2, 269-277 p.Article in journal (Refereed) Published
Abstract [en]

2-amino-5-chloropyridine (ACP) is a degradation product of zopiclone (ZOP) and may be formed when blood specimens are stored. ZOP instability in blood makes interpretation of concentrations difficult especially in cases of prolonged sample storage. This study investigated how ACP could be used to estimate the original concentration of ZOP in authentic samples. For that purpose, an analytical LC-MS/MS method for the quantitation of ACP, ZOP and the metabolite Ndesmethylzopiclone (NDZOP) in blood was validated. The method was then applied to investigate ACP formation, ZOP and NDZOP degradation in stored ZOP post-dosed authentic whole blood and two mathematical models were used to calculate the original concentration of ZOP. During storage, ACP was formed in amounts equimolar to the ZOP and NDZOP degradation. Results from samples in which ACP had been formed were used to test two models to estimate the original ZOP concentration. The correlation tests of the models showed strong correlations to the original ZOP concentration (r=0.960 and r=0.955) with p<0.01. This study showed that the equimolar degradation of ZOP and NDZOP to ACP could be used to estimate the original concentration of the unstable ZOP.

Place, publisher, year, edition, pages
Springer, 2015
Keyword
Degradation; Forensic toxicology; 2-amino-5-chloropyridine; Zopiclone; LC-MS/MS
National Category
Medical and Health Sciences Forensic Science
Identifiers
urn:nbn:se:liu:diva-105820 (URN)10.1007/s00414-014-1049-2 (DOI)000350032800007 ()25069820 (PubMedID)
Note

The article title of this article was in Manuscript: LC-MS/MS determination of 2-amino-5-chloropyridine to estimate the original zopiclone concentration in stored whole blood.

Available from: 2014-04-08 Created: 2014-04-08 Last updated: 2017-12-05Bibliographically approved

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