Validation of oral fluid as a matrix for drug detection
New testing procedures used as an aid for law enforcement are subject to intensive scrutiny in the courts. In recent years in workplace drug testing there has been a shift away from using traditional specimens (i.e urine) for drug testing and monitoring and a move to employing less invasive testing using oral fluid. Whilst it is now widely accepted that drugs can be detected in oral fluid and devices are now available to facilitate analysis of drugs in this matrix, our understanding of the behaviour of drugs in the mouth and oral secretions is far from complete. Since the introduction of oral fluid drug testing in the late 1990’s it has been observed that some drugs appear to be present at higher than expected concentrations, often at concentrations that would be fatal if they were in blood. Clearly some extra process is occurring in addition to drugs entering the oral fluid by simple blood and saliva partitioning. Little is really known about the physiology of drugs in the mouth and limited understanding of drug elimination via the mouth poses a problem to forensic toxicologists with the interpretation of analytical results in relation to an individual’s drug use or the possible effects that the drug may be exhibiting on that individual. The work described in this thesis is aimed at increasing our understanding of the factors and processes concerning the deposition, secretion and detection of drugs in oral fluid and enhancing our ability to interpret the results of analysis in this matrix. The objective of this study was to explore how high drug concentrations can be deposited in the mouth tissues and oral fluid together with other factors that may influence drug detection in order to assist with the interpretation of testing results. To test the hypothesis that drug depots form within the mouth, preliminary screening methods in combination with confirmatory techniques such as GC-MS and LCMS/ MS were employed. The development of an immunohistochemical method was successfully demonstrated for the detection and visualisation of cocaine and opiates (heroin and morphine) in porcine and mouse tissue. The work undertaken in this thesis showed that elevated drug concentrations can be observed when drugs are consumed via oral administration either in form of an oral solution or smoking. Immunohistochemical analysis in combination with confirmatory techniques demonstrated that drugs such as cocaine and opioids can bind to oral tissue and be subsequently released over time, therefore has the potential to contribute to the drug concentration in oral fluid. Although this is not an issue under legislation that forbids the presence of drugs or as a check for drug compliance or abstinence, it must be considered in relation to the interpretation of results in more complex forensic cases.
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