Toxicology Week 1

Sarah Heinrichs

Notes for Chemical Toxicology

Dr. Pistos

Spring 2025

1.22.2025 – Day 1

Toxicology: The study of the adverse effects of xenobiotics on the human body when they are present at toxic concentrations

Pharmacology: The study of the effects of chemical xenobiotics on the human body at therapeutic concentrations

Xenobiotics: any substance which is foreign to the body

Paracelsus (1493-1541): Everything is poisonous, the only difference is the dose

Mathieu Orfila (1787-1853): The father of forensic toxicology

>The first scientific treatise on the detection of poisons and their effects on animals

>Established six classes of poisons

>First use of forensic toxicology

Alexander Gettler (1918-1959): The Father of Forensic Toxicology in the U.S.

National Safety Council (NSC): The science that studies the poisonous or toxic properties of substances

Williams and Burson: The study of chemical and physical agents that produce adverse responses in the biological systems with which they interact

Casarett and Doull: The study of the adverse effect of chemical agents on biological systems. The study of adverse effects of xenobiotics on living organisms.

Forensic Toxicology: Human performance, postmortem, DFC (drug facilitated crime), and Forensic Drug testing

PED: Performance Enhancing Drugs

World Anti-Doping Agency (WADA)

DUI:Driving under the influence (of alcohol)

DUID: Driving under the influence of Drugs

Toxicology: The study of how natural or man-made poisons cause undesirable effects in living organisms

Adverse effects: Those that are damaging to either the survival or the normal function of the individual

Toxicity: The degree to which a substance is poisonous or can cause injury

Toxic: Poisonous or deadly effects on the body caused by any form of consumption

Toxicant: Any chemical that can injure or kill humans, animals, or plants; a poison

Toxin: Toxic substances produced naturally

Toxic symptom:Any feeling or sign indicating the presence of poison in the system

Toxic effects: Health effects that occur due to exposure to a toxic substance

Selective toxicity: Means that a chemical will produce injury to one kind of living matter without harming another form of life

How does toxicity develop: A substance must come into contact with some part of the body

Dose: the amount of chemical that enters the body

Dose-response: A relationship between exposure and health effect that can be established by measuring the response relative to an increasing dose

Threshold dose (NOAEL or LOEL): a dose or exposure level below which the harmful or adverse effects of a substance are not seen in a population

NOAEL and LOEL: used in experimental toxicology to perform toxicity risk assessment studies

NOAEL: No Observed Adverse Effect Level

LOEL: Lowest Observed Effect Level

Individual susceptibility: difference in types of responses to hazardous substances between people

Adverse Effects: occur when two drugs are competing for the same receptor

(Additive/Synergistic/Potentiation/Antagonism)

EXAMPLE

Drug A: 0 units response

Drug B: 3 units response

Drug C: 5 units response

Drug D: 10 units response

________________________________

Drug A + B = 5 units → potentiation

Drug B + C = 8 units → additivity

Drug C + D = 20 units → synergism

1.24.2025 – Day 2

Dose-Response relationship

• ED50

  • Is the dose that would be predicted to be effective or have a therapeutic benefit in 50% of the population

• TD50

  • Is the dose that would be predicted to produce a toxic response in 50% of the population

• LD50

  • Is the dose that would predict death in 50% of the population

• Therapeutic Index: TD50/ED50

  • The higher it is the more safe a dose is

Dose-Response Curve for Alcohol

Factors Affecting Toxicity

• Extrinsic Factors: occur outside the body

  • Dose

  • Route of exposure

  • Frequency

  • Duration

  • Concentration

  • Absorption? Metabolism? Accumulation? Distribution? Elimination?

  • Properties of the chemical

    • Hydrophobicity = increased lipophilicity

      • A drug which is very hydrophobic is highly lipophilic and is retained more in the body and excreted very slowly

    • Hydrophilicity = decreased lipophilicity

      • If a molecule is hydrophilic, the substance remains more in the bloodstream and is excreted much faster in the body

• Intrinsic Factors: occur within an individual organism

  • Susceptibility

    • Each one of us responds very differently

    • This is part of why individualization of treatment is so important

  • Age

    • Children tend to have faster metabolism with certain drugs

    • Not all enzymes are fully developed in children, so they can't actually metabolize every drug yet like an adult can

    • Elderly people have less structured proteins, which is what drugs want to bind to

  • Body size

    • Think of alcohol’s effects on a 200lb man versus a 120lb man

      • CH3CH2OH is ethanol

      • Polar, wants to be in water

  • Gender

    • Water in men: 55%

    • Water in men: 68%

      • This is why women are more affected by alcohol than men

Sub-disciplines of Toxicology

1. Mechanistic: elucidates the cellular and biochemical effects of toxins

2. Descriptive: uses results of animal experiments to predict harmful effects to humans

3. Occupational Toxicology: Combines occupational medicine and occupational hygiene

4. Environmental Toxicology: Integrates toxicology with sub-disciplines such as ecology, wildlife and aquatic biology, environmental chemistry.

5. Food Toxicology: Is involved in delivering a safe and edible supply of food to the consumer

6. Regulatory Toxicology: Gathers and evaluates existing toxicological information to establish concentration-based standards of “safe” exposure

7. Clinical: the study of interrelationships between toxin exposure and disease states (diagnosis & therapeutic intervention)

8. Forensic: concerned with medico-legal consequences of exposure to a toxic substance or a toxin.

Forensic Toxicology

• Has this person been poisoned?

• What is the identity of the poison?

• How was it administered?

• What are its effects?

• Was it a dangerous or lethal dose?

  • Includes measurement of alcohol, drugs and other toxic substances in biological specimens and interpretation of results in a medicolegal context.

What if the poison is not known?

Toxicological investigations:

• Human and animal testing

• Human performance

• Postmortem toxicology

• Unbiased scientific expertise in court

Cause of death (COD) is the natural disease or injury that led to physiologic changes resulting in death.

Manner of death (MOD) is the classification/categorization used for how the death came about

• MOD commonly has 5 categories

  • Natural

  • Homicide

  • Suicide

  • Accident

  • Undetermined

• Some jurisdictions have an additional MOD: therapeutic complication

• Medical examiner cases can also be pending further studies

Mechanism of death is the immediate physiologic derangement resulting in death (e.g. hemorrhage, sepsis, asphyxia), which is not etiologically specific.

Types of samples : Documentation : Sample preparation

Blood Components:

• Plasma

• Red cells

• White cells

• Platelets

  • Spin down to get serum

Plasma vs. Serum

• Plasma is the same as serum, but plasma contains an anticoagulant (usually EDTA) while the serum tubes do not. Neither contain red blood cells

You cannot separate plasma post-mortem, so you must work with whole blood that is typically clotted

1.27.2025 - Day 3: Class Cancelled

1.29.2025 - Day 4: 

Alternative Samples:

• Gastric content

  • Useful after overdoses

• organs/tissues

  • When the body is found after blood has already clotted, this can be useful

• Bile

  • When blood and urine are not available, since we prefer to work with biological fluid instead of tissue, we will use bile

• Vitreous fluid

  • Gold standard sample when testing alcohol

  • Remains for days after death, is in a protected cavity so not affected by any microbes

• Brain

• Hair 

  • Tells us about long-term use of the substance

  • The testing itself requires high expertise and is very vigorous

  • Passive exposure of substance into the hair

• Nails 

Orfila guidelines that are still in use:

• Case History

• All submitted evidential material must be examined

• All required ID tests must be done according to STA (Systematic Toxicological Analysis)

1.31.2025 - Day 5:

• Usage of CRM, blanks and QC samples

  • Caymen’s chemicals

  • Cerilient

Method development-validation for the determination of doA in biological fluids

• Sample preparation

• Analytical technique

• Validation

Accreditation: ISO17O25

• SOPs

• Instruments

• Procedures

• Methods

• PTS

  • Proficiency Testing Scheme

Classifications

1. Narcotics or Opiates (ex. Heroin, morphine)

2. Cannabis

3. CNS stimulants (ex. Amphetamines, cocaine)

4. CNS depressants (ex. TCAD)

5. Hallucinogens (ex. LSD, PCP)

6. NPSs

   1. Novel Psychoactive Substances

7. Therapeutics

8. Doping (performance enhancement) substances

9. Pesticides

10. Sexual abuse drugs

11. Alcohol

12. Inhalants (ex. Fuel, glue)

13. CO

14. Metals

PK/PD

Pharmacokinetics: The study of what the body does to the drug

Pharmacodynamics: The study of what the drug does to the body

• Absorption

  • Bioavailability (BA): The actual amount of the drug which enters into the bloodstream

  • (actual amount entering bloodstream) / (dose) (100) = %BA

Factors affecting BA:

1. Route of administration

2. Formulation

   1. Chemical properties of the substance

   2. Type: chalky powder vs gel capsule

2.3.2025 - Day 6:

• Metabolism

• Distribution

• Excretion

  • Urine, kidneys

    • Within the kidneys, the nephrons filter everything

  • Routes of excretion

    • Urine

    • Bile

    • Feces

    • Skin (sweat)

    • Lungs (exhalation)

• Elimination Kinetics

When any substance is very lipophilic, that means it is very hydrophobic and it is less hydrophilic

2.5.2025 - Day 7

Pharmacokinetics - Pharmacodynamics

• Routes of administration

• Rate of absorption

• Tmax

• Relation of dose with blood and tissue concentrations

• Rates of metabolism and clearance

Pharmacokinetic Parameters

• Area under the curve

  • Trapezoidal Rule

• Cmax is the max concentration

• Tmax is the time taken to reach Cmax

• T1/2 is the time taken to reach the half life elimination of the drug

Separation of plasma/serum from whole blood

→ centrifuge sample >2500RPM for 10 minutes 

When a drug enters into the bloodstream, plasma protein binding occurs

• Albumin is the most important protein in this process 

Always the free amount of the drug in plasma is the one which applies the pharmacological effect, not the binding portion of the drug ends up in the receptors.

Volume Distributions and Potency

High volume distribution (Vd) (>5 L/kg)

→ indicates that the drug is hydrophobic (aka lipophilic)

→ indicates that the drug is highly partitioned/distributed in the body’s tissues/organs

→ goes to the tissues because they are more hydrophobic/lipophilic 

Benzodiazepines has a structure that allows you to either increase the potency or increase the duration of action

→ with the exception of R5, R1-R6 can be substituted with very electronegative atoms such as chlorine, and electron withdrawing groups such as that will increase the potency.

Delta9-THC has one of the highest Vd’s (10 L/kg)

→ will stay in the blood longer

Low Vd (<5 L/kg)

→ indicates that the drug is hydrophilic and is highly partitioned/distributed in blood

→ since it's in the blood, it's easier to get eliminated faster

Absolute Bioavailability: the absolute amount that enters the bloodstream. 

The amount of administration which provides 100% bioavailability is intravenous

=(amount of drug in blood after oral administration)/(amount of drug in blood after IV administration)

Relative Bioavailability = (Amount of drug in blood after administration of drug A)/(Amount of drug in blood after administration of drug B) **[using the SAME route of administration]

a. Proteins

b. double -layer of phospholipids

This favors the diffusion of nonpolar molec.

The more hydrophobic a molec. is, the better

Factors affecting bioavailability

• Solubility

• Concentration

• Surface area

• Blood supply

• pH

*Concept of bioequivalence

Henderson-Hasselbalch Equations

Acidic drug’s pH = pka + log [ionized]/[unionized]

Basic drug’s pH = pka + log [unionized]/[ionized]

A medium with an acidic pH favors the absorption of an organic acidic drug

A medium with a basic pH favors the absorption of an organic base drug

2.7.2025 - Day 8

 Bioequivalence studies: studies which are conducted by the manufacturers of generic drugs.

• Generic drug manufacturers must be able to prove that their formulation is similar to the original one (to the reference drug).

• In these studies, one group will be administered the reference drug, and the other group will be administered the test drug. In “Phase Two” of testing, these two groups flip.

• Volunteers stay in clinic

• Blood tests are conducted

• Curves of conc vs time are made, and if the area under the two curves match, then they are similar.

→ Vitamins A, D, E, K are lipophilic, so you should take these with fatty food because it helps them absorb.

→ Tetracyclines (a type of antibiotic) should not be taken with milk, because it'll form a complex with the calcium in the molecule and not absorb.

ADME: Absorption, Distribution, Metabolism, Excretion

→ Distribution is movement of a medication from circulation to the body's tissues. The higher the volume of distribution, the more it absorbs into the tissues and the less it absorbs into the blood.

Albumin is the most important plasma binding protein