Cannabis - Forensic Toxicology (Lecture Notes) PDF

1 Cannabis - Forensic Toxicology Graham R. Jones, Ph.D. Former Chief Toxicologist, OCME & Clinical Professor, U of A Faculty of Medicine and Dentistry Edmonton, Alberta, Canada What do most forensic labs measure? • Delta-9-tetrahydrocannabinol (∆9-THC) • Highly lipid soluble • Usually measured i...

1 Cannabis - Forensic Toxicology Graham R. Jones, Ph.D. Former Chief Toxicologist, OCME & Clinical Professor, U of A Faculty of Medicine and Dentistry Edmonton, Alberta, Canada What do most forensic labs measure? • Delta-9-tetrahydrocannabinol (∆9-THC) • Highly lipid soluble • Usually measured in whole blood • Majority of the research was conducted in serum or plasma • THC blood:plasma ratio ~0.5 - 0.6 • 11-Hydroxytetrahydrocannabinol (11-OH-THC) • Pharmacologically “active” • Concentrations are higher after oral ingestion (first pass effect) • 11-Carboxytetrahydrocannabinol (THC-COOH) • Inactive metabolite • Forms water soluble glucuronide metabolite • Majority present as the glucuronide • Most labs measure the unconjugated THC-COOH (in blood) • Most urine testing labs (workplace) measure the total THC-COOH • Most forensic labs do NOT measure cannabidiol (CBD) ‘Emerging’ in the last couple of years* • Delta-8-tetrahydrocannabinol (∆8-THC) • Low concentrations natural present in Cannabis • Slightly less potent than ∆9-THC abd similar side-effects than ∆9-THC • Challenging to separate from ∆9-THC analytically • Delta-10-tetrahydrocannabinol (10-THC) • Positional isomer of ∆9-THC not usually present in Cannabis • Less potent than ∆9-THC(?) • Tetrahydrocannabiphorol (THC-P) • Much more potent (~30x) than ∆9-THC; not present in Cannabis • O-Acetyl-delta-9-tetrahydrocannbinol (THC-O) • Up to 3 x more potent than ∆9-THC; not present in Cannabis • May have hallucinogenic effects at high doses Other “Cannabis” Cannabinoids • Over 100 cannabinoids naturally present in cannabis • Cannabidiol (CBD) • Can be up to 40% of cannabis plant extract • Has been studied to treat anxiety, cognition, movement disorders, pain and epilepsy disorders • Little if any psychoactivity • May modify the effects of THC if both are present • Legal in the USA (cannabis extracts are not) • Cannabinol (CBN) • Mildly psychoactive, but present in only small amounts in cannabis • Is a metabolite of delta-9-THC Effects of Δ-9-Tetrahydrocannabinol • Psychoactive effects include • a state of relaxation, perhaps euphoria • facility for philosophical thinking, introspection • anxiety and paranoia • increase in heart rate and hunger, reddening of eyes • reduces nausea and vomiting • impaired motor skills; • Impaired judgment of time and distance Note: unless otherwise stated, any reference to “THC” in this lecture refers to ∆9-THC Interpretation...not as ‘easy’ as with alcohol • For alcohol (ethanol) there is a generally ‘direct’ correlation between blood concentration and “effect” (e.g. impairment) • Ethanol: can estimate “dose” from a blood level and can estimate a blood level from a dose • For THC, the correlation Data from: https://www.infrastructure.gov.au/roads/safety/publications/1997/pdf/Speed_Risk_1.pdf between blood level and “effect” is very poor except in the very early stages of smoking Pharmacokinetics of THC & metabolites • The “peak” ∆9-THC represents cessation of smoking • Note, the “research” cigarette only 3.55% THC • In most people, duration of the ‘high’ lasts 2 – 6 hours, i.e. much longer than the blood THC concentration is elevated Huestis MA, Henningfield JE, Cone EJ. 1992 Delta-9-THC • Short distribution half- life • Long elimination halflife resulting in “baseline” blood THC concentrations up to 7 ng/mL after heavy chronic use CH Ashton, Br J Psychiatry, Volume 178: 101-6, 2001 EW Schwilke, EL Larschner, RH Lowe, WD Darwin, MA Huestis, SOFT Abstract 23, NC Oct 2007 8 Cannabis – Forensic / Postmortem Aspects Canadian Criminal Code - Cannabis • Part I of Bill C-46, came into force on June 21, 2018: • an offence for (low-level) THC concentrations of 2 ng/mL to • • • • less than 5 ng/mL, within 2 hours of driving. an offence for higher-level THC concentrations of 5 ng/mL or more, within 2 hours of driving. an offence that recognizes the effects of combined marijuana and alcohol consumption; 50 mg of alcohol per 100 mL blood plus 2.5 ng/mL or more of THC within 2 hours of driving. “per se” limits that have little correlation with “effect or degree of actual impairment”. Recognizes that THC has a short half-life in blood and that it could take police up to 2 hours to get a blood sample drawn. 11 But with THC it can get complicated in civil cases • THC has a relatively short half-life in blood • But a longer half-life in the brain • i.e. where THC has its primary effect related to impairment • And it has a MUCH longer half-life in the body • Lawyers will ask: • What does the blood THC level mean? • Is there a blood alcohol equivalent? • Does a blood concentration of ‘X’ ng/mL mean they were impaired? 12 Delta-9-THC: The Past ‘Wisdom’* • The following used to be held as accepted facts: • THC always drops to near zero a few hours after last smoke • “Blood” THC >2-3 ng/mL consistent with recent use (within 6 h) • You can use THC:THC-COOH ratio to estimate the time of last use • Little postmortem change • …NOT ANY MORE Huestis, M.A and Smith, M.L 2007 13 THC: What we now know … • Baseline blood THC several hours after smoking: • typically < 2 ng/mL in light smokers (<1 after 24 h) • can be > 5 ng/mL in heavy smokers (may be >10) • in one study 1.2 – 5.5 ng/mL 7 days after last use • very high body burden of THC slowly released into blood • Refers to LIVING people! 14 THC Postmortem – It’s More Complex • THC undergoes postmortem redistribution (i.e. can increase after death) • PM femoral blood THC can be MUCH higher in postmortem blood than pre-mortem (‘clinical’) blood • THC concentrates in muscle tissue and may be redistributing postmortem • But much larger effect may be the presence of fat in the postmortem blood drawn 15 Case 1: Aircraft Pilot with THC* • Young commercial pilot flew a small passenger plane into a hillside: “controlled flight into terrain” • Pilot killed on impact or soon after; 2 passengers survived • Pilot toxicology positive for cannabis: • Pleural blood: THC 11.9 ng/mL; carboxy 41.8 ng/mL • Femoral blood: THC 50.1 ng/mL; carboxy 21.6 ng/mL • Pilot could not have been smoking for at least 1 hour before the crash and probably closer to 2 hours • Did the blood THC reflect concentration in flight? • Was the pilot impaired by THC? 16 Case 2: ATV Death with THC* • Middle-aged man involved in an ATV roll-over • Taken to hospital with relatively minor injuries • Includes broken clavicle • Dies from lacerated subclavian vessel and massive bleed • Postmortem toxicology negative except for cannabis: • Antemortem blood THC 14 ng/mL; carboxy 110 ng/mL • Time: 2 hours post-accident • PM femoral blood THC 31 ng/mL; carboxy 19 ng/mL • Time: 68 hours post-accident, after 60 – 66 hours in ICU 17 Case 3: Stabbing victim with THC* • Young man stabbed to death; short survival time • PM Toxicology (blood): • Ethanol, cocaine, levamisole, phenacetin, cannabinoids • Central blood THC 3.5 ng/mL; carboxy 11.8 ng/mL • Femoral blood THC 37.1 ng/mL; carboxy 8.4 ng/mL • Huh? • Elevated femoral blood THC likely due to contamination with “fat” containing sequestered THC from current and past smoking Postmortem blood is not always a reliable sample Remember – THC is very fat soluble!! LEGALIZATION OF CANNABIS Interpretation can be quite complex and may affect both criminal and civil case litigation! SYNTHETIC CANNABINOIDS (AKA CANNABIMIMETICS; AKA “SPICE”, “K2” ETC) 21 “Spice” – Synthetic Cannabinoids • Aka Cannabimimetics • Chemicals impregnated into various dried plant materials • Synthetic chemicals that may or may not be closely related to the structure of delta-9-THC – Interacts with the cannabinoid receptors – Partial agonist activity at the cannabinoid receptor CB1 located mainly in the central nervous system – and the CB2 receptor, mainly in cells of the immune system • Four primary series – JWH (John W. Huffman, funded by NIDA for medical research) – AM (Alexandros Makriyannis, Northeastern University) – CP (research chemists at Pfizer) – HU (Raphael Mechoulam, the Hebrew University) • Many do not have true “THC” effects 22 Cannabimimetic Properties • Similar to Cannabis (hence “…mimetic”), but some may have more intense effect in ability to produce psychosis. • Psychoactive effects include • a state of relaxation, perhaps euphoria • facility for philosophical thinking, introspection • anxiety and paranoia; also • increase in heart rate and hunger, reddening of eyes • reduces nausea and vomiting • impaired motor skills; judging time and distance 23 Adverse effects of synthetic cannabinoids • Psychiatric • Psychosis (new-onset or exacerbation of pre-existing disease), agitation, anxiety, irritability, confusion, aggression, suicidality, memory changes, tolerance, withdrawal, dependence • Cardiovascular • Hypertension, tachycardia, ST-segment changes, chest pain, myocardial infarction, tachyarrhythmia • Neurologic • Generalized seizures, somnolence, brisk reflexes • Gastrointestinal • Nausea, vomiting, anorexia, increased appetite • Other • Hypokalemia, conjunctival injection (‘blood shot’ eyes), hyperglycemia, acute kidney injury, xerostomia (dry mouth), diaphoresis • Ref: Five things to know about synthetic cannabinoids.CMAJ, February 18, 2014, 186(3) 24 * 25 * 26 Cannabimimetic Analysis • Can be difficult! • Very low blood concentrations • Extensively metabolized • Over 200 possible structures • They keep changing as regulations change • Screening methods do not detect all • Need high-end methods for confirmation • e.g. LC/MS/MS • Relatively difficult and time-consuming to develop 27 Metabolism of JWH-18 – Clearance from blood* 28 Prevalence of different cannabimimetics over 3.5 years * 29 Risk Factors for Users • Downside: don’t know what you are getting • May vary from batch to batch even with the same name and label – substance and dose • Toxicity will vary tremendously depending on dose and the individual • For most ‘designer’ drugs little is known about toxicity and longterm effects 30 Canada vs. USA – The Differences • Canada: • Federal drug laws (Controlled Drugs and Substances Act – CDSA) • Specific named substances, but chemically related drugs that may have a similar pharmacological effect are similarly controlled (specific substances do not always have to be named) • USA: • DEA (Drug Enforcement Administration) has “federal” rules, but slow to add new substances • Did have Federal Analogue Act 1986 but sometimes difficult to get a prosecution • e.g. what is an analogue (how similar is it to a scheduled drug) • Stop the Importation and Trafficking of Synthetic Analogues Act of 2017 Individual states can make individual drugs illegal, but that was a slow “ad hoc” process that did not usually address “analogues”