Introduction to Toxicology and Important Definitions

Introduction to Toxicology

• Toxicology is the study of the adverse effects of chemicals on living organisms.
• Toxicologists examine the nature of these effects, including their cellular, biochemical, and molecular mechanisms of action, and assess the probability of their occurrence.

Toxicology Testing

• Toxicology testing, also known as safety testing or toxicity testing, is conducted to determine the degree to which a substance can damage a living or non-living organism.
• Acute toxicity tests involve a single dose in each animal on one occasion to determine gross behavior and LD50 or median lethal dose.
• Chronic tests involve dosing two species, one rodent and one non-rodent, daily for six months.
• Sub-acute tests involve dosing animals daily, starting at around expected therapeutic level and increasing stepwise every two to three days until toxic signs are observed.

Toxicants and Poisons

• Toxicants are substances that produce adverse biological effects of any nature, and may be chemical or physical in nature.
• Toxins are specific proteins produced by living organisms, such as mushroom toxins, which exhibit immediate effects.
• Poisons are toxicants that cause immediate death or illness when experienced in very small amounts.

Mechanisms of Toxicology

• Mechanistic toxicology identifies the cellular, biochemical, and molecular mechanisms by which chemicals exert toxic effects on living organisms.
• Descriptive toxicology is concerned with toxicity testing, which provides information for safety evaluation and regulatory requirements.
• Regulatory toxicology decides whether a drug or another chemical poses a sufficiently low risk to be marketed for a stated purpose.

Specialized Areas of Toxicology

• Environmental toxicology focuses on the impacts of chemical pollutants in the environment on biological organisms.
• Workplace drug testing is conducted for administrative purposes, and results are often used as evidence in court.
• Diagnostic or hospital (clinical) drug testing is conducted to assist in medical treatment.
• Forensic toxicological analysis is conducted for medical-legal purposes, including death and criminal investigations.

Toxic Effects

• The dose makes the poison, and all substances are poisons; there is none that is not a poison.
• The right dose differentiates a poison from a remedy, according to Paracelsus (1493–1541).
• Immediate toxic effects occur or develop rapidly after a single administration of a substance, whereas delayed toxic effects occur after the lapse of some period of time.
• Reversible toxic effects occur when a chemical produces pathological injury to a tissue, and the ability of that tissue to regenerate largely determines whether the effect is reversible or irreversible.

Interactions of Chemicals

• Additive effects occur when the combined effect of two chemicals is equal to the sum of the effects of each agent given alone.
• Synergistic effects occur when the combined effects of two chemicals are much greater than the sum of the effects of each agent given alone.

Spectrum of Undesired Effects

• Allergic reactions occur when a chemical combines with an endogenous protein to form an antigen (or immunogen), leading to an immunologically mediated adverse reaction to a chemical.

This quiz covers the basic introduction to toxicology, including important definitions such as toxicology, toxicologist, and toxicology testing. Test your knowledge on the adverse effects of chemicals on living organisms and the process of assessing the probability of such effects.