Difficulties associated with the interpretation of postmortem toxicology

While postmortem (PM) toxicology results provide valuable information towards ascertaining both the cause and manner of death in coronial cases, there are also significant difficulties associated with the interpretation of PM drug levels. Such difficulties are influenced by several pharmacokinetic and pharmacodynamic factors including PM redistribution, diffusion, site-to-site variability in drug levels, different drug properties and metabolism, bacterial activity, genetic polymorphisms, tolerance, resuscitation efforts, underlying conditions, and the toxicity profile of cases (i.e. single- or mixed-drug toxicity). A large body of research has been dedicated for better understanding and even quantifying the influence of these factors on PM drug levels. For example, several investigative matrices have been developed as potential indicators of PM redistribution, but they have limited practical value. Reference tables of clinically relevant therapeutic, toxic, and potentially fatal drug concentrations have also been compiled, but these unfortunately do not provide reliable reference values for PM toxicology. More recent research has focused on developing databases of peripheral PM drug levels for a variety of case-types to increase transferability to real-life cases and improve interpretations. Changes to drug levels after death are inevitable and unavoidable. As such, guidelines and practices will continue to evolve as we further our understanding of such phenomena.

Post-mortem Redistribution of Alprazolam in Rats

The post-mortem toxicological findings may be misinterpreted, if the drug undergoes substantial post-mortem redistribution. As alprazolam is one of the most frequently evaluated drug for legal/forensic reasons in drug-related fatalities, we studied possible changes in alprazolam distribution after death in a rat model. Rats were sacrificed 30 minutes after alprazolam administration. Blood and tissue samples from 8 animals per sampling time were collected at 0, 2, 6, and 24 h after death. The experimental samples were assayed for alprazolam using validated UHPLC-PDA method. Median blood alprazolam concentrations increased approximately 2 times compared with ante-mortem levels due to the redistribution during early post-mortem phase and then slowly decreased with a half-life of 60.7 h. The highest alprazolam tissue concentrations were found in fat and liver and the lowest levels were observed in lungs and brain. The median amount of alprazolam deposited in the lungs was relatively stable over the 24-h post-mortem period, while in heart, liver and kidney the deposited proportion of administered dose increased by 43-48% in comparison with ante-mortem values indicating continuous accumulation of alprazolam into these tissues. These results provide evidence needed for the interpretation of toxicological results in alprazolam-related fatalities and demonstrate modest alprazolam post-mortem redistribution.

A Mechanism-Based Forensic Investigation into the Postmortem Redistribution of Morphine

The interpretation of postmortem drug levels is complicated by the change in drug blood levels during the postmortem period, a phenomenon known as postmortem drug redistribution. We investigated the postmortem redistribution (PMR) of morphine, morphine-3-glucuronide and normorphine in the rat. Morphine (10 mg/kg) was intravenously injected into rats, followed by euthanasia 1 h post-injection. The carcasses were placed in a supine position at room temperature, and tissues including heart blood, femoral blood, liver, lung and brain were collected at different time points: 0, 8, 16 or 24 h postmortem. The samples were analyzed with a validated (following modified Scientific Working Group for Forensic Toxicology (SWGTOX) (20) guidelines) liquid chromatography-tandem mass spectrometry method. The use of a mechanism-based approach (involving the used set doses of drug with the study performed in controlled environment) to assess PMR using systematic and statistical analyses provides important information that has not previously been presented in PMR literature. While previous human studies focus on central to peripheral ratios as well as peripheral to tissue ratio, this work focused on the change in morphine and metabolite concentrations over the course of the postmortem interval in relation to each other in addition to the comparison to additional matrices at each postmortem interval. Postmortem redistribution was identified in several tissues across the postmortem interval; however, there was minimal statistical difference observed among each matrix at a given postmortem interval with the exception of normorphine and morphine-3-glucuronide. Combined, our study provides a valuable resource and reference information that can aide toxicologists, medical examiners or coroners when assessing postmortem drug concentrations of morphine and metabolites when they are making determinations of cause of death.

Classical Mistakes in Forensic Toxicology Made by Forensic Pathologists

The forensic pathologist interprets the toxicology results in the setting of the entire death investigation. This review focuses on potential errors by the forensic pathologist with regard to toxicology analysis encountered with death investigation. These include mistakes of determining the cause of death based solely on the drug concentration and failure to consider the postmortem nature of the specimen when interpreting results. The forensic toxicologist does analytical toxicology; i.e., determining what drug(s) is/are present and in what concentration. The forensic pathologist does interpretive toxicology, which requires consideration of the decedent's medical history, the circumstances surrounding death, the environment of the death, the autopsy findings, and the results of the analytical toxicology. Forensic pathologists must communicate with the forensic toxicologists, understand their limitations, and collect proper specimens. Providing appropriate clinical information to the toxicologists will result in more timely and thorough toxicological analysis. Toxicologic results should be included on the death certificate only when they make a pathologic contribution to death.

Post-mortem clinical pharmacology

Clinical pharmacology assumes that deductions can be made about the concentrations of drugs from a knowledge of the pharmacokinetic parameters in an individual; and that the effects are related to the measured concentration. Post-mortem changes render the assumptions of clinical pharmacology largely invalid, and make the interpretation of concentrations measured in post-mortem samples difficult or impossible. Qualitative tests can show the presence of substances that were not present in life, and can fail to detect substances that led to death. Quantitative analysis is subject to error in itself, and because post-mortem concentrations vary in largely unpredictable ways with the site and time of sampling, as a result of the phenomenon of post-mortem redistribution. Consequently, compilations of 'lethal concentrations' are misleading. There is a lack of adequate studies of the true relationship between fatal events and the concentrations that can be measured subsequently, but without such studies, clinical pharmacologists and others should be wary of interpreting post-mortem measurements.

Post-mortem toxicology

Studies examining post-mortem processes are difficult to conduct since changes will have already occurred when the body arrives at the mortuary. While control of collection site for blood can minimize changes in concentration it is very difficult to conduct experiments in humans aimed at understanding the mechanisms and determining the extent of such changes. The use of appropriate animal models can be useful in this regard providing the species and conditions are carefully chosen. Pharmacokinetic studies in humans are also very useful for understanding the changes in drug concentration with time in blood (and other fluids) and also for improving our understanding of drug effects. Unfortunately, doses of illicit drugs that can be given are relatively low to guarantee safety hence extrapolations are made to real life situations. Individual case studies can be useful to describe an unusual or particularly interesting circumstances but little useful information can be obtained when trying to ascertain the role of competing factors, e.g. role of individual drugs when multiple drugs are present, varying toxicity between route of administration, and the role of age or natural disease when drugs are also present. Epidemiological approaches by reviewing large numbers of related cases are the most powerful tool to obtain this information. All of these studies need to operate under the ethical and legal framework appropriate for a jurisdiction. This paper discusses the relative merits of scientific approaches to research in post-mortem toxicology and provides guidance on the most appropriate techniques for future studies.

Interpretation of analytical toxicology results in life and at postmortem

Interpretation of analytical toxicology results from live patients is sometimes difficult. Possible factors may be related to: (i) the nature of the poison(s) present; (ii) sample collection, transport and storage; (iii) the analytical methodology used; (iv) the circumstances of exposure; (v) mechanical factors such as trauma or inhalation of stomach contents; and (vi) pharmacological factors such as tolerance or synergy. In some circumstances, detection of a drug or other poison may suffice to prove exposure. At the other extreme, the interpretation of individual measurements may be simplified by regulation. Examples here include whole blood alcohol (ethanol) in regard to driving a motor vehicle and blood lead assays performed to assess occupational exposure. With pharmaceuticals, the plasma or serum concentrations of drugs and metabolites attained during treatment often provide a basis for the interpretation of quantitative measurements. With illicit drugs, comparative information from casework may be all that is available. Postmortem toxicology is an especially complex area since changes in the composition of fluids such as blood depending on the site of collection from the body and the time elapsed since death, amongst other factors, may influence the result obtained. This review presents information to assist in the interpretation of analytical results, especially regarding postmortem toxicology. Collection and analysis of not only peripheral blood, but also other fluids/tissues is usually important in postmortem work. Alcohol, for example, can be either lost from, or produced in, blood especially if there has been significant trauma, hence measurements in urine or vitreous humour are needed to confirm the reliability of a blood result. Measurement of metabolites may also be valuable in individual cases.

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.

Postmortem digoxin-like immunoreactive substances (DLIS) in patients not treated with digoxin

Endogenous digoxin-like immunoreactive substances (DLIS) cross-react in immunoassays of digoxin. The postmortem rise in digoxin levels in patients treated with the drug may be due to its redistribution. It is unclear what is the contribution of DLIS to this increase and whether DLIS are present postmortem in patients not treated with digoxin. The objectives of this study were to determine whether DLIS are present after death in patients not treated with digoxin, whether a postmortem increase in DLIS is detectable and whether sampling site can affect DLIS concentrations. DLIS (measured as digoxin, TDx Abott) were determined in blood samples drawn antemortem from ICU patients; postmortem samples from femoral artery and cardiac chambers were taken at least 12 h after the death of these same patients. DLIS concentrations > or = 0.2 ng/ml were measured in 44 and 40% of patients antemortem and postmortem (femoral), respectively. No difference was found in DLIS levels between antemortem and postmortem femoral and cardiac samples. Age, ICU stay and postmortem sampling time did not affect the postmortem increase in DLIS. None of the levels was in the toxic range. DLIS may be present after death and their concentration does not increase postmortem. The interpretation of postmortem digoxin concentrations that fall in the therapeutic range should be done cautiously; such measurable levels do not necessarily indicate misuse or malicious intent even in patients who had not been treated with the drug.

Postmortem changes and pharmacokinetics: review of the literature and case report

OBJECTIVE

To review the mechanisms and sequence of events that occur during ischemia and cell death and following death of the human body. The impact of these postmortem events on the distribution and pharmacokinetic behavior of drugs is described. The case study presented illustrates a possible situation where such postmortem changes could have affected the pharmacokinetics of procainamide.

DATA SOURCES

English-language journal articles and reference texts identified from pertinent data sources.

DATA SYNTHESIS

Postmortem changes in the human body begin at the cellular level with the onset of ischemia. As the length of time of ischemia increases and death ensues, more changes occur and lead to deterioration in tissue and organ function. These changes may affect the pharmacokinetic and distribution behavior of certain drugs. Drugs particularly affected are those whose distribution is dependent on molecular size, lipophilicity, pH, energy-dependent transport, and tissue binding. Such drugs include the tricyclic antidepressants, digoxin, and cimetidine. Other drugs with similar characteristics, such as procainamide, may also demonstrate like changes in distribution and pharmacokinetics.

CONCLUSIONS

When measuring drug concentrations after death, it is important to consider the phenomenon of postmortem redistribution. Postmortem drug concentrations may not be a true reflection of antemortem concentrations and as a result, wrong conclusions could be made about the cause of death. More studies characterizing the postmortem distribution and pharmacokinetic characteristics of specific drugs are necessary.

Postmortem disposition of morphine in rats

The antemortem and postmortem distribution of morphine was studied in rats for the purpose of establishing whether drug distribution is altered after death. Samples were examined for free and total morphine concentration, pH and water content at 0-96 h after death. Morphine was administered antemortem at various intervals. All groups of rats studied showed a significant (P less than 0.05) increase in postmortem cardiac blood morphine concentrations. These changes, which are detectable within 5 min after death are likely to be related to an observed, rapid decrease in cardiac blood pH from 7.34 +/- 0.02 to 6.74 +/- 0.05. Significant increases in free morphine levels were, also, observed 24 and 96 h after death in liver, heart and forebrain while urine morphine levels decreased. The liver showed the greatest increase (20-fold) in free morphine levels 96 h after death, while hindbrain levels did not significantly change. Bacterial hydrolysis of morphine glucuronides accounted only in part for the observed increase in free morphine concentration. Postmortem fluid movement and pH-dependent drug partitioning was detected. It would appear that several mechanisms are responsible for postmortem drug distribution. Understanding the mechanisms and patterns responsible may eventually lead to better choices of postmortem tissue which may better represent antemortem drug levels.

Interpretation of excessive serum concentrations of digoxin in children

Between January 1981 and April 1984, excessive serum concentrations of digoxin (5 ng/ml or higher) were recorded in 47 children, aged 2 days to 16 years. In 10 patients, the high concentrations were measured 9.25 to 48 hours after death and were significantly higher than antemortem levels in all cases (8.3 +/- 2.4 (+/- standard deviation) postmortem vs 3.3 +/- 1.5 antemortem, less than 0.0001). In 15 patients (40.5% of the living patients) serum concentrations of 5 ng/ml or higher reflected sampling errors; drug levels were monitored too closely to the administration of a dose. None of these children had toxic manifestations of digoxin. In 10 patients, the excessive concentrations were associated with renal failure and a prolonged elimination half-life (T1/2) of digoxin; in 3 of these patients, there were signs of digoxin toxicity. Six cases were caused by digoxin overdose (accidental ingestions, pharmacy error and a suicide attempt). In 6 additional cases, the existence of an endogenous digoxin-like substance (EDLS) was shown to contribute to the excessive levels of the drug. One case could be attributed to digoxin-amiodarone interaction. In 10 of 37 living patients, digoxin toxicity was diagnosed. After excluding the 15 sampling errors and 6 cases with EDLS, this represents 63% of the cases. There was a good correlation between digoxin elimination T1/2 and serum creatine concentrations (r = 0.71, p less than 0.01). The above observations suggest that excessive serum concentrations of digoxin may not necessarily reflect potentially toxic levels.(ABSTRACT TRUNCATED AT 250 WORDS)