Drugs of Abuse in Oral Fluid and Post-Mortem Endogenous Blood Concentrations of Gamma-Hydroxybutyrate (GHB)

Research output: ThesisDoctoral Thesis


Oral fluid is a versatile matrix that is proving more popular within forensic toxicology. Its use is multifaceted, and is the preferred matrix in therapeutic drug monitoring and roadside testing of drivers suspected to be under the influence of drugs. Benefits including the difficulty of adulteration, the ease and non-invasiveness of sample collection, the range of analytes that can be detected and decent correlations between concentrations in blood or plasma and oral fluid are some of the reasons for its attractiveness to practitioners and forensic toxicologists. Most often, oral fluid is collected using collection devices which can often include a stabilising buffer. When new collection devices are introduced to the market it is important that their applicability to drug testing is investigated to show they are fit for purpose. One of the newest collection devices on the market is the NeoSAL™ collection device from Neogen. This collector was gravimetrically assessed for oral fluid volume collection and drug recovery. Collection volume adequacy of the NeoSAL™ device was compared to two commonly used, commercially available, collection devices: namely the Immunalysis Quantisal™ and the OraSure Intercept® i2™ collection devices. Results showed that the NeoSAL™ device is capable of collecting more than the volume stated by the manufacturer, similar to the Intercept® i2™ which also over-collected, whereas the Quanitsal™ device collected the stated volume. Drug recoveries from the NeoSAL™ collection pad for all drugs investigated in this thesis exceeded 57% (lower recoveries were observed for temazepam and diazepam). Although amphetamine and methamphetamines are not often abused or encountered in forensic samples in Scotland, they are a global problem and effects of abuse can negatively impact a person’s ability to drive by increasing recklessness and risk-taking. Neat and oral fluid collected using the NeoSAL™ device were used to develop and partially validate a method for the quantification of amphetamine, methamphetamine, MDMA, MDA and MDEA using GC-MS. MDEA was also assessed, but did not give acceptable results for accuracy and precision. A short-term autosampler stability study for the four acceptable analytes showed that they were stable on the autosampler for up to 48 hours (~ 19 °C). Opioid and benzodiazepine drugs are two of the most commonly abused drug groups in Scotland. They are often taken synchronously, and the latter is the most commonly prescribed and encountered drug group in Scotland. With the continuation of opioid epidemics and large numbers of people in opioid-treatment programmes, it is beneficial to have a sensitive and selective method that can be used for the simultaneous analysis of these two drug groups. Research has shown that both drug groups are common in drivers, although symptoms of use include loss of coordination, sedation, and drowsiness. An SPE procedure using LC-MS/MS detection was optimised for the extraction for the concurrent analysis of 5 benzodiazepines and 5 opioid drugs. The method was validated according to the guidelines for method validation in forensic toxicology (SWGTOX 2013). The validated method was successfully applied to paired oral fluid and blood samples collected from 16 benzodiazepine users. The NeoSAL™ collection device showed that good recoveries (>57% for all analytes but diazepam and temazepam), and good detection rates for the 10 analytes studied was possible. Oral fluid and blood results showed a good correlation between the analytes detected and in most cases where there was no overlap, it was possible to explain these discrepancies by metabolism, detection windows, low sample volume, and sensitivities of the respective analytical methods used. Gamma-hydroxybutyrate (GHB) is a short-chain fatty acid that is not only endogenous to the mammalian body, but can also be prescribed medicinally and be used as a drug of abuse. A stability study (over 56 days) of GHB in neat oral fluid was carried out as none have been published in the literature. GHB stability is an important factor to assess due to its short detection window in the more traditional matrices blood and urine. A simple protein precipitation extraction procedure was used, and the analytical GC-MS method was adapted from the in-house method for analysis of GHB/beta-hydroxybutyrate (BHB) in blood. The method was partially validated and the stability of GHB was assessed at two concentrations at three temperatures (fridge ~ 4 °C, freezer ~ -21 °C, and room temperature ~ 20 °C). GHB appeared to be stable at all three temperatures for up to 56 days. Endogenous post-mortem blood concentrations of GHB have been widely studied, however debate is still existent regarding cut-off concentrations that should be applied. Problematic interpretation arises from the post-mortem production, and inter- and intra- individual variation of GHB in the human body. 1811 cases between 2010 and 2016, which did not implicate GHB in the cause of death or where GHB was not suspected to have been used, were extracted from the in-house Forensic Medicine and Science (FMS) database. The majority of cases (51%) were deaths related to alcohol abuse. 76% of cases showed GHB concentrations < 30 mg/L, and 94% of all cases had concentrations of less than 50 mg/L. Results also suggest that the use of a preservative may prevent in vitro formation of post-mortem GHB. 112 cases showed GHB concentrations in excess of 50 mg/L with advanced decomposition, therefore suggesting that decomposition changes may increase GHB concentrations. This was the largest dataset that ever studied endogenous post-mortem GHB concentrations, and results highlight the difficulty when applying cut-off concentrations to distinguish post-mortem or exogenous and endogenous concentrations.
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • University of Glasgow
  • Wylie, Fiona, Supervisor, External person
  • Scott, Karen, Advisor, External person
Award date21 Jun 2018
Place of PublicationGlasgow
Publication statusPublished - 2017
Externally publishedYes


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