Forensic Toxicology Overview

Overview of Forensic Toxicology

• Forensic Toxicology involves the application of toxicology and related fields to aid medical or legal investigations of death, poisoning, and drug use.
• Key areas:
  • How drugs and toxins are handled by the body (ADME)
  • Methods for detection, identification, and quantification of substances by forensic toxicologists
  • Case studies focus on substances such as cocaine, ethanol, and THC.

Definition of Forensic Toxicology

• Wikipedia: Forensic toxicology utilizes toxicological science and analytical fields to assist in the investigation related to medical or legal circumstances, focusing on the interpretation of results rather than technologies used.
• Canadian Society of Forensic Science: Its focus is on studying harmful effects of drugs and chemicals on biological systems and interpreting results for legal matters.

Role of Forensic Toxicologists

• Responsibilities:
  • Detect and identify drugs/toxins in body fluids and tissues
  • Interpret biological consequences of detected substances
• Collaborative relationship with Analytical Toxicology and Analytical Chemistry.

Understanding Drugs and Toxins

• Definition:
  • A drug is any substance (other than a normal body constituent) that alters body functions.
• Quote from Paracelsus: “All substances are poisons; the right dose differentiates a poison from a remedy.”

Phases of Drug Handling (ADME)

Absorption

• Drugs must pass epithelial barriers to enter the body.
• Common Routes of Administration:
  • Gastrointestinal (GI) tract
  • Sublingual
  • Inhalation
  • Dermal (skin)
  • Injection (subcutaneous, intramuscular, intravenous)
• Factors Influencing Absorption:
  • Physicochemical properties of the drug
  • Administration route affects the speed of entry into the bloodstream

Distribution

• After absorption, drugs circulate in the bloodstream, distributing to tissues, including the brain.
• Blood concentrations serve as a surrogate measure of drug presence at target sites.
• Distribution variation depends on the administration method.

Metabolism (Biotransformation)

• Enzymes in body tissues, primarily the liver, catalyze the conversion of drugs into metabolites.
• Common reactions:
  • Oxidation, reduction, conjugation
• Implications for Forensic Toxicologists:
  • Knowledge of metabolites is crucial, as some drugs are only detectable in metabolic form.
  • Example: Cocaine is largely metabolized with only 1% excreted unchanged in urine.

Excretion

• Drugs are eliminated primarily via urine or feces, with some expelled through breath.
• Elimination depends on drug solubility; fat-soluble drugs are metabolized into water-soluble forms.
• Half-Life:
  • Influences how long effects of drugs persist; for example, cocaine has a half-life of 60-90 minutes, whereas THC can last 1.3 to 13 days.

Detecting and Measuring Drugs

• Sample Collection:
  • Living individuals: blood, urine, breath, hair
  • Deceased individuals: blood, urine, tissue samples
• Extraction Techniques:
  • Drugs must often be extracted from biological tissues into organic solvents for analysis.
• Measurement Techniques:
  • Initial screening assays: Thin layer chromatography, Gas chromatography, Immunoassay
  • Confirmatory tests: Gas chromatography/mass spectrometry (GC/MS) is the gold standard.

Interpretation of Results

• Assess the biological effects of detected substances:
  • Potential causes of death or behavioral influence
  • Presence or absence of therapeutic drugs affecting behavior
• Challenges in Forensic Toxicology:
  • Requires integration of various crime scene information for accurate analysis and result interpretation.

Ethanol (Alcohol Toxicology)

• Most commonly used and abused drug; poses legal implications due to its widespread regulation.
• ADME for Ethanol:
  • Water-soluble, absorbed quickly, distributes evenly in the bloodstream.
  • Metabolized primarily in the liver to carbon dioxide and water.

Blood Alcohol Concentration (BAC)

• BAC is a critical measure in legal or medical contexts, expressed as a percentage indicating the proportion of alcohol in blood.
• Example: A BAC of 0.10 means 0.10% of blood is alcohol.
• Influenced by factors such as body weight, sex, food intake, affecting the rate of absorption and intoxication levels.

Tetrahydrocannabinol (THC)

• Principal psychoactive substance in Cannabis; very lipid-soluble with low gastrointestinal absorption (5-10%).
• Absorbed rapidly from the lungs with a quick onset of effects; concentrations in fatty tissues can lead to prolonged biological effects.
• Detection of THC is complex, particularly regarding impairment, as psychological effects diminish faster than THC presence in the body.