Vitreous humour as a complementary sample to blood for the detection/confirmation of diazepam: ante-mortem and post-mortem studies in an animal model

The quantification of medical or toxic substances in vitreous humour (VH) could be very useful in forensic toxicology when blood sample determinations are impossible due to absence or deterioration. However, few studies have been made in this area and even fewer have tried to find a relationship between drug levels in both samples. To determine a correlation ratio between blood and VH diazepam (DZ) levels, we performed an experimental study using rabbits administered with a sub-toxic dose of DZ under known and controlled conditions. Blood and VH samples were collected 0.5, 1, 2, 3 and 6 hours after the drug administration in order to determine DZ and its main active metabolite, desmethyldiazepam (DMD). In addition, we have studied an animal group sacrificed 2 hours after intramuscular (i.m.) drug administration with blood and VH collection 24 hours later, to evaluate the existence of possible post-mortem changes. After DZ administration, a fast absorption phase was observed with a plasma Cmax value 1 hour after, followed by a rapid concentration decrease, with a half-life of 1 hour, indicating that, besides elimination, a fast distribution to other organs and tissues and/or hepatic metabolism occurred. Diazepam Cmax value in VH was achieved between 1 and 2 hours, when plasma concentrations had already decreased to half the value. The plasma/VH DZ ratio calculated at this time was 10. In the post-mortem study, while plasma DZ concentration at 24 hours was smaller, DMD levels were higher than those at the time of death. In the VH, both DZ and DMD concentrations at 24 hours were higher than those obtained at the time of death. That is, in both fluids DZ and DMD concentrations were different from those at the time of death and post-mortem distribution and redistribution phenomena occurred. The combination of ante-mortem and post-mortem studies has allowed the determination of a correlation ratio for DZ in the rabbit of 6 x, comparing the concentrations in VH collected 24 hours after death with the concentrations detected in plasma at the time of death. This study opens new perspectives for the use of VH as a complementary sample to blood for DZ detection and confirmation. The putative relevance of the correlation ratio obtained, for forensic toxicology practice with medical substances, namely benzodiazepines, recommends further studies in humans.

Preanalytic aspects in postmortem toxicology

The preanalytic phase has been recognized to have a substantial role for the quality and reliability of analytical results, which very much depend on the type and quality of specimens provided. There are several unique challenges to select and collect specimens for postmortem toxicology investigation. Postmortem specimens may be numerous, and sample quality may be quite variable. An overview is given on specimens routinely collected as well as on alternative specimens that may provide additional information on the route of administration, a long term or a recent use/exposure to a drug or poison. Autolytic and putrefactive changes limit the selection and utility of specimens. Some data from case reports as well as experimental investigations on drug degradation and/or formation during putrefaction are discussed. Diffusion processes as well as postmortem degradation or formation may influence ethanol concentration in autopsy specimens. Formalin fixation of specimens or embalmment of the corpse may cause considerable changes of initial drug levels. These changes are due to alterations of the biological matrix as well as to dilution of a sample, release or degradation of the drug or poison. Most important seems a conversion of desmethyl metabolites to the parent drug. Some general requirements for postmortem sampling are given based on references about specimen collection issues, for a harmonized protocol for sampling in suspected poisonings or drug-related deaths does not exist. The advantages and disadvantages of specimen preservation are shortly discussed. Storage stability is another important issue to be considered. Instability can either derive from physical, chemical or metabolic processes. The knowledge on degradation mechanisms may enable the forensic toxicologist to target the right substance, which may be a major break down product in the investigation of highly labile compounds. Although it is impossible to eliminate all interfering factors or influences occurring during the preanalytic phase, their consideration should facilitate the assessment of sample quality and the analytical result obtained from that sample.

Postmortem toxicology of drugs of abuse

Conducting toxicology on post-mortem specimens provides a number of very significant challenges to the scientist. The range of additional specimens include tissues such as decomposing blood and other tissues, hair, muscle, fat, lung, and even larvae feeding on the host require special techniques to isolate a foreign substance and allow detection without interference from the matrix. A number of drugs of abuse are unstable in the post-mortem environment that requires careful consideration when trying to interpret their significance. Heroin, morphine glucuronides, cocaine and the benzodiazepines are particularly prone to degradation. Moreover, redistributive process can significantly alter the concentration of drugs, particularly those with a higher tissue concentration than the surrounding blood. The designer amphetamines, methadone and other potent opioids will increase their concentration in blood post-mortem. These processes together with the development of tolerance means that no concentration of a drug of abuse can be interpreted in isolation without a thorough examination of the relevant circumstances and after the conduct of a post-mortem to eliminate or corroborate relevant factors that could impact on the drug concentration and the possible effect of a substance on the body. This article reviews particular toxicological issues associated with the more common drugs of abuse such as the amphetamines, cannabinoids, cocaine, opioids and the benzodiazepines.

Postmortem drug analysis: analytical and toxicological aspects

Publications focusing on the analysis of postmortem specimens for the presence of drugs were reviewed with particular reference to systematic toxicological analysis. Specimens included blood, liver, other solid specimens, and fly larvae. Extraction techniques published during the past 10 years most commonly used traditional solvent extraction techniques. High-performance liquid chromatography coupled to multichannel wavelength detection was most commonly used, which would easily lend itself to liquid chromatography-mass spectrometry. There were few practical differences in the assays validated for a range of postmortem specimens to those in other forms of forensic toxicology, unless substantially decomposed tissue was used. When putrefied specimens were analyzed, a back-extraction or other form of specimen cleanup was recommended to reduce interfering substances. Many immunoassays designed for urine have been adapted for use in blood and tissue homogenates. Immunoassays designed for blood analysis, however, are likely to have more useful cutoff values than immunoassays optimized for urine testing. Postmortem specimens provide less stability for a number of drugs than other types of specimens. This is particularly a problem for cocaine, heroin, and some antidepressants, antipsychotics, and benzodiazepines. A number of artifacts occur postmortem, which affects the concentration of drug in specimens. This includes postmortem redistribution for drugs with a high tissue concentration relative to blood. Consequently, the likely extent of any change in concentration is relevant to the interpretation of doses and drug effects.

Assessment of the acuteness of heroin deaths from the analysis of multiple blood specimens

Data was compiled from 126 morphine-involved cases investigated by the Office of the Chief Medical Examiner, State of Maryland, USA. An investigation was conducted into whether comparison of morphine concentrations from a central and peripheral site could be used to determine whether a morphine death was acute or delayed. Fifty cases were identified as 'acute' because the urine free morphine concentration by radioimmunoassay (RIA) was less than 25 ng/mL; 76 cases were classified as 'random' because they had a urine morphine concentration greater than 25 ng/mL by RIA. The average heart blood to peripheral blood morphine concentration ratio in the acute deaths was 1.40. The average heart blood to peripheral blood morphine concentration ratio in the random deaths was 1.18. Because there was considerable overlap between the two groups of data, the authors conclude that it was not possible to predict 'acute' opiate intoxication deaths versus 'delayed' deaths when the only information available is heart and peripheral blood free morphine concentrations.

Postmortem diffusion of drugs from the bladder into femoral venous blood

We describe significantly elevated drug concentrations in the femoral venous blood due probably to postmortem diffusion from the bladder. A 16-year-old deceased male was found in a shallow ditch in winter. The estimated postmortem interval was 9 days and putrefaction was not advanced. The cardiac chambers contained fluid and coagulated blood and a small amount of buffy coat clots. Diffused hemorrhages were found in the gastric mucosa. The bladder contained approximately 600 ml of clear urine. Gas chromatographic-mass spectrometric analysis of the urine disclosed allylisopropylacetylurea (a fatty acid ureide sedative), diphenhydramine, chlorpheniramine and dihydrocodeine. The cause of death was considered to be drowning due to a drug overdose and cold exposure. The concentrations of diphenhydramine, free dihydrocodeine and total dihydrocodeine in the femoral venous blood (1.89, 3.27 and 3.30 microg/ml, respectively) were much higher than those in blood from the right cardiac chambers (0.294, 0.237 and 0.240 microg/ml, respectively). Urine concentrations of diphenhydramine, free dihydrocodeine and total dihydrocodeine were 22.6, 37.3 and 43.1 microg/ml, respectively. The stomach contained negligible amounts of diphenhydramine, free dihydrocodeine and total dihydrocodeine (0.029, 0.018 and 0.024 mg, respectively); concentrations of these drugs in the femoral muscle were 0.270, 0.246 and 0.314 microg/g, respectively. These results indicate that postmortem diffusion of diphenhydramine and dihydrocodeine from the bladder resulted in the elevated concentrations of these drugs in the femoral venous blood. Not only high urinary drug concentrations but also a large volume of urine in the bladder might accelerate the postmortem diffusion.