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Chemistry

Drugs of Abuse

Studying drugs of abuse in toxicology calls for understanding their core properties. In this section, we look at the properties of drugs of abuse

General Properties of Drugs of Abuse

  • Definition: Drugs of abuse are substances that are used for non-medical purposes, often for their psychoactive effects, and can lead to dependence, addiction, and adverse health consequences
  • Classification: Drugs of abuse can be classified into several categories based on their pharmacological effects:
    • Opioids: Produce analgesia, euphoria, and sedation (e.g., heroin, morphine, oxycodone)
    • Stimulants: Increase alertness, energy, and euphoria (e.g., cocaine, amphetamines, methamphetamine)
    • Cannabinoids: Produce relaxation, altered perception, and euphoria (e.g., marijuana, hashish)
    • Hallucinogens: Alter perception, thought, and mood (e.g., LSD, psilocybin, MDMA)
    • Depressants: Slow down brain activity, producing relaxation and sedation (e.g., alcohol, benzodiazepines, barbiturates)
    • Inhalants: Volatile substances that produce psychoactive effects when inhaled (e.g., solvents, aerosols, gases)
  • Common Properties
    • Psychoactive Effects: Alter mood, perception, and cognition
    • Reinforcing Effects: Produce pleasurable or rewarding experiences that promote continued use
    • Addictive Potential: Can lead to dependence and addiction

Chemical Properties of Drugs of Abuse

  • Structural Diversity: Drugs of abuse exhibit significant structural diversity, encompassing a wide range of chemical classes
  • Functional Groups: They contain various functional groups, such as hydroxyl, amino, carbonyl, ester, and ether groups, which influence their solubility, binding properties, and metabolism
  • Basic or Acidic Character: Many drugs of abuse are weak bases or acids
  • Chirality: Some drugs of abuse are chiral molecules, existing as enantiomers or diastereomers with differing pharmacological activities
  • Chemical Stability: Varies widely depending on the specific drug and its formulation; storage conditions can affect stability

Physical Properties of Drugs of Abuse

  • Appearance: Crystalline solids, powders, liquids, or plant materials
  • Solubility: Varies depending on the specific drug and its chemical structure
  • Partition Coefficient (Log P): Indicates the relative affinity of a drug for lipid and aqueous phases
  • Ionization: Acidic or basic properties influence their absorption, distribution, and excretion
  • Protein Binding: Binding to plasma proteins (albumin, alpha-1-acid glycoprotein)
  • Melting Point: Characteristic property for identification and purity assessment
  • Boiling Point: Important for volatile substances
  • Hygroscopicity: Some drugs of abuse are hygroscopic, absorbing moisture from the air

Specific Drugs of Abuse

Opioids (e.g., Morphine)

  • Definition: Opioids are a class of drugs that bind to opioid receptors in the central nervous system, producing analgesia, euphoria, and sedation
  • Examples: Morphine, codeine, heroin, oxycodone, hydrocodone, fentanyl
  • Chemical Structure: Complex alkaloids with a characteristic morphinan ring structure
  • Molecular Weight: Varies depending on the specific opioid (e.g., morphine: 285.34 g/mol)
  • Solubility: Varies depending on the specific opioid, but generally soluble in water or alcohol
  • Ionization: Weak bases
  • Protein Binding: Varies depending on the specific opioid
  • Pharmacokinetic Implications: Rapid absorption after oral, intravenous, or intramuscular administration; extensive metabolism in the liver; renal excretion

Stimulants (e.g., Cocaine)

  • Definition: Stimulants are a class of drugs that increase alertness, energy, and euphoria by affecting the central nervous system
  • Examples: Cocaine, amphetamine, methamphetamine, methylphenidate
  • Chemical Structure: Amphetamines are derivatives of phenethylamine; cocaine is a benzoylmethylecgonine
  • Molecular Weight: Varies depending on the specific stimulant (e.g., cocaine: 303.36 g/mol)
  • Solubility: Varies depending on the specific stimulant, but generally soluble in water or alcohol
  • Ionization: Weak bases
  • Protein Binding: Varies depending on the specific stimulant
  • Pharmacokinetic Implications: Rapid absorption after various routes of administration (oral, intranasal, intravenous, smoking); metabolized in the liver; excreted in the urine

Cannabinoids (e.g., THC)

  • Definition: Cannabinoids are a class of chemical compounds that act on cannabinoid receptors in cells that alter neurotransmitter release in the brain
  • Examples: Δ9-tetrahydrocannabinol (THC), cannabidiol (CBD), cannabinol (CBN)
  • Chemical Structure: Tricyclic compounds with a characteristic dibenzopyran ring system
  • Molecular Weight: Varies depending on the specific cannabinoid (e.g., THC: 314.46 g/mol)
  • Solubility: Highly lipophilic and poorly soluble in water
  • Ionization: Neutral
  • Protein Binding: Highly protein-bound
  • Pharmacokinetic Implications: Rapid absorption when smoked or vaporized; slow and variable absorption after oral administration; extensive metabolism in the liver; excreted in the feces and urine

Hallucinogens (e.g., LSD)

  • Definition: Hallucinogens are a class of drugs that alter perception, thought, and mood
  • Examples: Lysergic acid diethylamide (LSD), psilocybin, mescaline, 3,4-methylenedioxymethamphetamine (MDMA)
  • Chemical Structure: Highly variable, depending on the specific hallucinogen
  • Molecular Weight: Varies depending on the specific hallucinogen (e.g., LSD: 328.43 g/mol)
  • Solubility: Varies depending on the specific hallucinogen
  • Ionization: Some are basic, some are neutral
  • Protein Binding: Varies depending on the specific hallucinogen
  • Pharmacokinetic Implications: Rapid absorption after oral administration; metabolized in the liver; excreted in the urine

Depressants (e.g., Benzodiazepines)

  • Definition: Depressants are a class of drugs that slow down brain activity, producing relaxation and sedation
  • Examples: Alcohol, benzodiazepines (diazepam, alprazolam, lorazepam), barbiturates (phenobarbital, secobarbital)
  • Chemical Structure: Benzodiazepines contain a benzene ring fused to a diazepine ring; barbiturates are derivatives of barbituric acid
  • Molecular Weight: Varies depending on the specific depressant
  • Solubility: Varies depending on the specific depressant
  • Ionization: Weak acids or bases
  • Protein Binding: Varies depending on the specific depressant
  • Pharmacokinetic Implications: Rapid absorption after oral administration; metabolized in the liver; excreted in the urine

Analytical Significance

  • Selection of Analytical Method: Physical and chemical properties guide the selection of appropriate analytical methods
  • Sample Preparation: Solubility and stability determine the optimal sample preparation techniques
  • Interpretation of Results: Understanding metabolism and excretion helps interpret analytical results and assess the severity of poisoning

Clinical Significance

  • Accurate Diagnosis: Prompt and accurate identification of the ingested drug is crucial for appropriate treatment
  • Assessment of Severity: Measurement of drug concentrations helps assess the severity of poisoning and guide clinical management
  • Monitoring of Treatment: Serial measurements of drug concentrations are used to monitor the effectiveness of treatment and guide further interventions

Summary Table of Drugs of Abuse and their properties

Drug Class Molecular Weight Lipophilicity Metabolism Excretion Common Analytical Tests
Opioids Morphine 285.34 g/mol Variable Liver Urine Immunoassay, GC-MS, LC-MS
Stimulants Cocaine 303.36 g/mol Variable Liver Urine Immunoassay, GC-MS, LC-MS
Cannabinoids THC 314.46 g/mol High Liver Feces/Urine Immunoassay, GC-MS, LC-MS
Hallucinogens LSD 328.43 g/mol Variable Liver Urine GC-MS, LC-MS
Depressants Variable Variable Liver Urine Immunoassay, GC-MS, LC-MS

Key Terms

  • Drugs of Abuse: Substances used for non-medical purposes that can lead to dependence and addiction
  • Opioids: Analgesic drugs that bind to opioid receptors
  • Stimulants: Drugs that increase alertness and energy
  • Cannabinoids: Chemical compounds found in cannabis
  • Hallucinogens: Drugs that alter perception and thought
  • Depressants: Drugs that slow down brain activity
  • Toxicokinetics: The study of the movement of toxic substances within the body
  • Metabolism: The process by which the body chemically alters a substance
  • Excretion: The process by which the body eliminates a substance
  • Addiction: A chronic, relapsing brain disease characterized by compulsive drug seeking and use
  • Dependence: A state in which the body has adapted to a drug and experiences withdrawal symptoms upon cessation of use
  • Overdose: A toxic dose of a drug that can lead to serious health consequences or death
  • Analgesic: A medicine used to relieve pain
  • Illicit: Illegal activities