Postmortem Toxicology: An Overview PDF

Postmortem Toxicology: An Overview Graham R. Jones, Ph.D. Former Chief Toxicologist Office of the Chief Medical Examiner & Clinical Professor, Faculty of Medicine and Dentistry [email protected] Death Investigation • Medical Examiner system • Alberta • Manitoba • Nova Scotia • Newfoundland •...

Postmortem Toxicology: An Overview Graham R. Jones, Ph.D. Former Chief Toxicologist Office of the Chief Medical Examiner & Clinical Professor, Faculty of Medicine and Dentistry [email protected] Death Investigation • Medical Examiner system • Alberta • Manitoba • Nova Scotia • Newfoundland • Coroner system • • • • • • British Columbia Saskatchewan Ontario Quebec New Brunswick, PEI NWT, Nunavut, Yukon Medical Examiner system headed by a forensic pathologist Coroner system may or may not be headed by a physician Cause and Manner of Death • Cause of Death • Immediate MEDICAL cause of death • NOT circumstances • e.g. “blunt force trauma” rather than “motor vehicle accident” • Manner of Death • Specific categories • • • • • • Homicide Suicide Accident Natural Undetermined Unclassified (MAID deaths) Time of death? Not usually possible to determine with any accuracy. Examples… • Young man found dead in front of car in closed garage, with hood open and tools laid out. Death caused by carbon monoxide poisoning. • What is the manner of death? • Young woman with long history of depression crosses into the oncoming lane and collides with a semi-trailer headon. • What is the manner of death? Alberta Office of the Chief Medical Examiner • Offices • Edmonton and Calgary • Cases ~6500 / year • Total Alberta deaths ~32000 • Homicides ~80–100 /year • Toxicology • ~50 alcohol or CO only • ~5000 “full” toxicology Alberta – OCME Investigated Deaths ~6500 Medical Examiner Cases annually: Homicidal Suicidal Accidental Undetermined Natural ~2% (80 – 100) 12% 49% ~2% 34% Cases have increased substantially over the past 6 – 10 years!!! Other Forensic Laboratories • RCMP Labs in Vancouver, Edmonton, Ottawa • DNA, trace evidence (e.g. hair and fibre, accelerants), documents, firearms • RCMP Handle ONLY criminal cases • Ontario and Quebec have their own labs (and provincial police services) • Toxicology in other provinces handled by various other arrangements • Local hospital; provincial laboratory, U.S. private laboratory Why is Toxicology Important vs. Autopsy? Myth: • All drug overdoses will have evidence of “pill fragments” in the stomach. Fact: • Most fatalities due to drugs or poisons will not show specific signs at autopsy. An autopsy can rule out natural disease or trauma as the cause of death. Sometimes natural disease may be contributory. Postmortem: Cannot use serum or plasma • Whole blood • Vitreous • Urine • Liver • Stomach contents • Other tissues (sometimes: e.g. decomposition) • Hair (sometimes: e.g. criminal case) • Other “exhibits” (syringes, drinking glass) Blood • Most consistently available, abundant “fluid” • Postmortem blood usually partially to fully hemolyzed • Often not “homogeneous” throughout body • Not usually useful for biochemical tests • Drug concentrations can go up or down after death (depends on drug) • Drug concentrations should not be interpreted “in isolation” (more later) Vitreous Humor • Clear fluid from inside eye • Limited volume (~3 mL per eye); usually available • Very useful for alcohol • Can be useful for some drugs (e.g. cocaine, heroin, digoxin) • Cannot interpret as you would blood • Drug concentrations often lower than in blood – especially highly lipid soluble and protein-bound drugs (e.g. benzodiazepines, tricyclic antidepressants) Urine • Clear fluid, no protein and very little lipid (exception – decomposed bodies) • Urine not always available in postmortem cases • Concentrations of some drugs very high • Some drugs not excreted into urine due to extensive metabolism, but metabolites can be detected • Little or no relationship between urine drug concentration and pharmacological effect (exceptions alcohol and maybe some metals) • Cannot relate urine drug concentration and degree of impairment Liver • Always present, large amount of specimen • Need to make liquid preparation (homogenize) • High protein and lipid content can interfere • Drug concentrations don’t change much after death • Some exceptions: drugs may diffuse form stomach into liver if concentrations high; some drugs are unstable • Liver drugs concentrations are often much higher than in blood • Often useful to have BOTH liver and blood concentrations • Liver widely used in the past – but less now! Stomach Contents • Very variable from clear fluid to a “meal” • Drug concentrations can be very high • Need to relate drug concentration to total volume • Interpretation: total AMOUNT, not concentration • Drug (and/or metabolite) can be in stomach after parenteral use (e.g. i/m, i/v) due to secretion in gastric juice • Presence in stomach does not prove oral use Stomach - Example • Therapeutic range for phenytoin in blood is 10 – 20 mg/l • Gastric concentration is 150 mg/l – toxic? NO! • 150 mg/l may be 15 mg/100 ml, if volume of gastric is 100 ml • Could mean partially absorbed 100 mg dose… Other Specimens… • Bile, CSF or virtually any fluid • Lungs, kidney, muscle or any solid tissue • Bone, nails, hair • Injection sites • Need “control” site away from suspected injection site • Can be difficult to prove injection site if elapsed time – especially if i/v injection • Principle: most drugs are distributed to virtually all fluids and tissue in the body!!! Other “exhibits”… • Syringes • Can indicate what was injected (useful if heroin) • Drinking glasses • Can be useful in drug facilitated sexual assault cases • Can indicate manner of death in suicide • Bottles • Can indicate source of a poison Chain of Custody • A means of tracking exhibits (e.g. specimens) from the point and time of collection to analysis and ultimately disposal. • Involves place/location, date, time and persons (e.g. analysts). • Purpose: to demonstrate that analysis and reporting was performed on the stated exhibit/specimen. • Usually involves a reasonable degree of physical security, such as locked storage (e.g. fridge/freezer, locker), secured facility (e.g. laboratory) and restricted access (authorised personnel; escorted visitors). • Physical or electronic log of those entering and leaving the facility. • Authorised staff may have an electronic key-card. Preventing Deaths - Carbon Monoxide Some are obvious… Carbon monoxide binds to hemoglobin 200x stronger than oxygen! Carbon Monoxide Deaths Some sources are less obvious… Why postmortem toxicology is “different”… Severe motor vehicle accident: Ethanol not detected, but… Urine METHANOL 530 mg% Liver 190, 300 mg% Spleen 20, 70 mg% Explanation? Postmortem Fermentation Blood Vitreous Blood ON ITS OWN is UNRELIABLE as a specimen for assessing the presence of alcohol at the time of death. Can get postmortem BAC up to “legal limit” due to fermentation; in RARE circumstances >300 mg%. Postmortem Redistribution Main mechanism • Release and diffusion of drugs from the major organs • Occurs as cells die, pH changes and protein binding weakens • Time and concentration dependent • Candidates: • Drugs with a high volume of distribution typically >5L/kg • Drugs with ‘Basic’ character (e.g form HCl salts) • Increases of 2 – 10 fold or greater possible • Order of increasing magnitude of PM redistribution: • Cardiac > subclavian > femoral > antemortem Example of the Problem of Postmortem Redistribution  48 y.o. woman with severe heart disease and history of depression found unresponsive at home  Taken to hospital but could not be resuscitated (i.e. dead)  Blood taken at hospital by local medical examiner  However, local ME could not decide whether COD was natural or drug overdose – autopsy ordered  Blood also taken again at autopsy (12 – 18 h later) Example of the Problem of Postmortem Redistribution - Results Antemortem blood (DOA) Femoral blood (at hospital) Cardiac blood (at autopsy) Liver Stomach Amitriptyline 0.10 0.20 2.20 18 trace Nortriptyline 0.34 0.37 5.10 29 trace Concentrations of amitriptyline and nortriptyline ~10x higher in blood taken at autopsy than blood collected at the hospital COD is “natural” – elevated autopsy blood drug concentrations due to postmortem redistribution! Delayed Deaths  Depressants (narcotics, sedatives) with or without alcohol can cause hypoxic brain damage ◦ Resuscitation and hospitalization for hours or days can lead to low or near absent levels ◦ Even without resuscitation, drugs can lead to prolonged coma prior to death, and low drug levels ◦ Near-fatal ethanol can clear in <24h  Delayed deaths also a factor with acetaminophen, ethylene glycol and methanol  Antemortem specimens important!! Impaired Metabolism • Can be due to: • Genetic impairment due to enzyme deficiency • e.g. cytochrome P4502D6 in 7-10% Caucasians • Drug-Drug impairment of enzyme system • e.g. impairment by SSRIs of CYP4502D6 • Impairment due to high single drug concentration • Impairment due to reduced liver function (age, alcohol) Accumulation of ADHD Medication in a Young Boy      7 year old boy with severe attention deficit disorder Medications: imipramine (150 mg hs); valproate (250 mg hs). Collapsed suddenly at school; resuscitation unsuccessful. No prior history of serious side effects Autopsy negative; toxicology indicates “imipramine poisoning”??? Imipramine Desipramine Cardiac blood 1.1 13 Femoral blood 0.47 6 Liver 35 449 Antemortem Se 0.069 0.942 (15 min after collapse) mg/l or mg/kg Juvenile Imipramine Death 10- Hydroxyimipramine 2- Hydroxyimipramine HO (OH) N Hydroxydesipramines CPY3A4 (and conjugates) CYP2D6 N N N Imipramine CYP3A4 N Hydroxydesipramines Desipramine CPY2D6 (and conjugates) NH Fatal Drug Accumulation in a Young Manic Depressive • 21 y.o. university student living with parents • History of manic depression, but well controlled • Watching TV with father, but feeling unwell and went to bed early; 2 h later complained of nausea • 4 h later was heard to collapse and taken to hospital; died en route; resuscitation failed • All medication accounted for (no indication of “overdose”) • Prescribed: 900 mg chlorpromazine, 125 mg imipramine, 10 mg amphetamine • No cause of death at autopsy; toxicology… Fatal Drug Accumulation – Toxicology Results Femoral blood Liver Stomach Chlorpromazine 0.92 111 trace Imipramine 0.60 37 trace Desipramine 3.74 261 trace Results: mg/l or mg/kg 1. Liver levels VERY high (especially metabolite desipramine 2. Very high desipramine (metabolite) to imipramine suggests accumulation 3. Likely genetic (P4502D6) and/or drug-drug induced accumulation 4. All medications accounted for (none missing) Tolerance / Opiate Deaths • Interpretation of postmortem narcotic blood levels VERY VERY tricky! • Need to have some idea of degree of tolerance • If naïve user, interpretation easier • If prescribed, need medical record and/or pharmacy record • Need to know dose and duration of dosage • Preferably need “medication count” Methadone – Two Cases • Case 1: • 26 y.o. with dubious history of opiate addiction; new in methadone program • Dies over w/end after taking 4 x 40 mg methadone in ~48h • PM Blood methadone 0.34 mg/l (liver 4.6 mg/kg) • Witness evidence of sedation, loud snoring etc. • Found dead; no COD Case 1: Little or no tolerance • Case 2: • Young male; well established in methadone program • Daily dose 130 mg • Routine blood methadone 0.83 mg/l • Little or no sedation • Alive!! Case 2: Substantial tolerance Sudden opioid death? No! • 46 year old known drug dealer was rushed to hospital by an acquaintance; he died. WHY? HOW? • Postmortem blood • • • • • • • • • carfentanil = 0.73 ug/l fentanyl = 93 ug/l xylazine = 8.4 ug/l furanylfentanyl = detected acrylfentanyl = detected (urine only) methadone = 0.17 mg/l morphine / 6-MAM = detected (heroin) methamphetamine = 0.20 mg/l Cocaine / BZE = detected • Obviously very high opioid tolerance!! COD was gunshot wound!!! ‘Medical’ Tolerance of Fentanyl • Starting dose 25 ug/hour for chronic pain • Potentially fatal for non-tolerant patients – 100 ug/hour • This patient had 34 x 100 ug/h fentanyl patches • No clinically significant respiratory depression! • Admission blood fentanyl 173 ng/mL • (therapeutic ~0.5 – 5 ng/mL) European Journal of Pain (2001) 5: 325±331 Inefficacy of high-dose transdermal fentanyl in a patient with neuropathic pain Bleeker, Bremer, Dongelmans, van Dongen and Crul Interpreting Postmortem Toxicology is VERY Different from Clinical Toxicology! Difficulties of interpreting postmortem data Don’t know when drug last taken; rate of metabolism; rate of excretion, AND Don’t know if postmortem blood level of drug represents blood level at time of death. Some concentrations increase postmortem; some decrease. Therefore cannot reliably calculate dose. Don’t know tolerance of person to toxic effects of the drug. MUST consider autopsy findings, medical history, circumstances of death. How should you interpret toxicology results? • Interpret with FULL consideration of: • Circumstances of death • Post-death investigation including: • • • • Medical history Medication history Autopsy findings Toxicology on alternate specimens!! • If you don’t have enough information, either DON’T offer an interpretation, or give clear caveats! “Medication Counts” • For each important medication determine: • • • • • Number prescribed Date dispensed Dosage (e.g. tablets per day) Number remaining at death Calculate meds “unaccounted for” • Why? Suicide vs. “Build-up”…