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Problems of Forensic Sciences 2005  Vol. 64 (LXIV)  382-394
 
ANALYTICAL ISSUES IN FORENSIC TOXICOKINETICS

Helen KASTRISSIOS, Robert E. GAENSSLEN, Adam NEGRUSZ
Department of Biopharmaceutical Sciences, College of Pharmacy, University of Illinois, Chicago (United States of America)


Abstract

The two major aspects of forensic toxicology are: forensic drug and alcohol screening and interpretation, and post-mortem investigations. The important issues in forensic drug screening are accessibility of biological samples and the availability of sensitive and specific analytical methods for accurate detection, identification and quantification of specific chemical compounds. Although blood is the most common biological sample collected in clinical settings, its use in forensic drug screening is limited. Commonly, urine is preferred because higher drug concentrations are detectable in urine. A limitation of urine collection is that the sample may not be directly observed to be collected from a particular individual. Forensic drug screening has been performed using a variety of tissues, including hair, nails, sweat, saliva and breath and meconium. The primary goal of drug screening is to identify biological samples that contain specific drugs under investigation and to rapidly screen out samples that do not contain the drug. Sensitivity of the analytical technique is an important issue since chemicals may be present in trace amounts in biological specimens. Improvements in the sensitivity and specificity of analytical techniques have been achieved by combining chromatographic methods, in order to effect separations of compounds of interest from biological matrices, with microplate enzyme immunoassays or mass spectrometry. Confirmation (verification) analysis is a critical phase of the screening process. It provides an increased level of assurance that a false positive result has not been obtained in the initial screening phase. GC-MS is a commonly used confirmatory technique as it is specific for particular compounds and is quantitatively accurate and precise at low concentrations. The knowledge of xenobiotic’s route of administration, metabolism, tissue distribution, biological half live, biological markers of exposure, play an important role in selection of the most appropriate specimen for analysis and the choice of the most sensitive and specific analytical method. Stability of drugs in biological specimens is extremely important in forensic toxicology and should be always seriously considered when forensic samples are being collected. Post-mortem forensic investigations are performed on suspicion of drug overdose with either illicit or prescription drugs, and in cases of suicide or homicide due to poisoning with a variety of toxic substances. Drug and/or alcohol levels in death cases can be a major factor in helping determine cause and the culpabilities of participants in both criminal and civil legal proceedings. The timing of specimen collection is an important, although often unknown, factor because it is a determinant of drug stability, the extent of tissue decomposition, and the extent of drug redistribution. Post-mortem blood drug concentrations may not reflect ante-mortem drug concentrations due to the phenomenon of drug redistribution. Moreover, unabsorbed drug in the gastrointestinal tract and drug-rich tissues, particularly the liver and lungs, constitute reservoirs from which drugs may be released post-mortem. The other problems connected with the analysis of  post-mortem samples are drug stability and selection of the appropriate sample for analysis.


Key words

Toxicology; Drug screening; Post-mortem.


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