Introduction to toxicology: definitions and types MCQs With Answer

Introduction: Introduction to toxicology: definitions and types MCQs With Answer is designed for M.Pharm students preparing for advanced pharmacological and toxicological screening modules. This set of MCQs focuses on core toxicology concepts — clear definitions, classifications (acute, chronic, local, systemic, intrinsic, idiosyncratic), dose–response principles, toxicokinetics, common metrics (LD50, NOAEL, LOAEL), interaction types (synergism, potentiation, antagonism), and practical aspects like routes of exposure, biomarkers, target-organ toxicity and regulatory safety margins. Each question targets comprehension and application relevant to preclinical screening, risk assessment and experimental design. Use these items to reinforce conceptual clarity and exam readiness.

Q1. What is the most accurate general definition of toxicology?

• The study of the beneficial uses of drugs in human therapy
• The study of harmful effects of chemical, physical or biological agents on living organisms and the ecosystem
• The study of drug metabolism only
• The study of infectious disease transmission

Correct Answer: The study of harmful effects of chemical, physical or biological agents on living organisms and the ecosystem

Q2. Which term describes an adverse effect occurring shortly after a single or short-term exposure?

• Chronic toxicity
• Subchronic toxicity
• Acute toxicity
• Delayed toxicity

Correct Answer: Acute toxicity

Q3. Which metric represents the dose that kills 50% of a test population under defined conditions?

• NOAEL (No Observed Adverse Effect Level)
• LD50 (Lethal Dose 50)
• LOAEL (Lowest Observed Adverse Effect Level)
• TDI (Tolerable Daily Intake)

Correct Answer: LD50 (Lethal Dose 50)

Q4. Which classification refers to toxicity that is observed after repeated or continuous exposure for a large part of an organism’s life?

• Subacute toxicity
• Acute toxicity
• Chronic toxicity
• Immediate toxicity

Correct Answer: Chronic toxicity

Q5. What does NOAEL indicate in toxicological studies?

• The lowest dose causing death in animals
• The dose producing any observable effect
• The highest tested dose at which no adverse effects are observed
• The dose resulting in 50% inhibition of an enzyme

Correct Answer: The highest tested dose at which no adverse effects are observed

Q6. Which type of toxicity is characterized by genetic damage that may lead to cancer or heritable mutations?

• Neurotoxicity
• Genotoxicity
• Hepatotoxicity
• Dermatotoxicity

Correct Answer: Genotoxicity

Q7. Intrinsic toxicity differs from idiosyncratic toxicity because intrinsic toxicity is:

• Rare and unpredictable, independent of dose
• Species-specific only and not dose-related
• Directly dose-dependent and predictable based on mechanism
• Always immune-mediated

Correct Answer: Directly dose-dependent and predictable based on mechanism

Q8. Which phrase best describes bioaccumulation?

• Rapid metabolism and excretion of xenobiotics
• The build-up of a chemical in an organism over time faster than it is eliminated
• The immediate toxic response after a single high dose
• The process of conjugation in the liver

Correct Answer: The build-up of a chemical in an organism over time faster than it is eliminated

Q9. Which of the following is NOT a common route of toxicant exposure?

• Inhalation
• Dermal absorption
• Injection
• Endogenous synthesis

Correct Answer: Endogenous synthesis

Q10. The term ‘margin of safety’ in toxicology often refers to:

• The ratio of LD50 to effective therapeutic dose
• The difference between observed human toxicity and no-effect animal dose expressed as a factor
• The precise mechanism of toxicity at the cellular level
• The time between exposure and symptom onset

Correct Answer: The difference between observed human toxicity and no-effect animal dose expressed as a factor

Q11. Which interaction describes two chemicals producing an effect greater than the sum of their individual effects?

• Antagonism
• Potentiation
• Synergism
• Additivity

Correct Answer: Synergism

Q12. LOAEL in toxicological studies stands for:

• Lowest Observed Adverse Effect Level
• Lethal Organ Affecting Exposure Limit
• Lowest Observed Analytical Effect Limit
• Limit Of Acceptable Exposure Level

Correct Answer: Lowest Observed Adverse Effect Level

Q13. Which type of toxic effect specifically refers to damage to the developing fetus?

• Mutagenicity
• Teratogenicity
• Carcinogenicity
• Immunotoxicity

Correct Answer: Teratogenicity

Q14. Toxicokinetics primarily deals with which processes?

• Mechanisms of cellular damage caused by toxins
• Absorption, distribution, metabolism and excretion (ADME) of toxicants
• Statistical analysis of toxicology data only
• Formulation chemistry of drug products

Correct Answer: Absorption, distribution, metabolism and excretion (ADME) of toxicants

Q15. Which is the best description of an idiosyncratic toxic reaction?

• A predictable allergic reaction occurring at high doses
• A rare, unpredictable reaction often unrelated to dose and seen in susceptible individuals
• A dose-dependent tissue necrosis observed in all species
• A reaction exclusively due to drug contamination

Correct Answer: A rare, unpredictable reaction often unrelated to dose and seen in susceptible individuals

Q16. In a dose–response relationship, the threshold dose is defined as:

• The dose at which 50% of subjects respond
• The lowest dose at which a measurable response occurs
• The maximum tolerated dose in animals
• The dose causing immediate lethality

Correct Answer: The lowest dose at which a measurable response occurs

Q17. Which biomarker would most directly indicate exposure rather than effect?

• Altered enzyme activity in the liver
• Parent compound concentration in blood or urine
• Histopathological lesions in kidney tissue
• Decreased platelet count

Correct Answer: Parent compound concentration in blood or urine

Q18. Carcinogenicity testing in preclinical screening primarily assesses:

• The potential of a compound to cause acute nausea
• The potential of a compound to induce tumors after long-term exposure
• Immediate skin irritation potential
• Short-term behavioral changes in rodents

Correct Answer: The potential of a compound to induce tumors after long-term exposure

Q19. Which regulatory concept uses uncertainty (safety) factors to extrapolate animal NOAELs to human exposure limits?

• Benchmark dose modeling without factors
• Applying physiologically based pharmacokinetic (PBPK) models only
• Use of safety/uncertainty factors to derive acceptable daily intakes
• Direct use of animal LD50 values as human exposure limits

Correct Answer: Use of safety/uncertainty factors to derive acceptable daily intakes

Q20. Which statement best contrasts hazard with risk in toxicology?

• Hazard is the probability of exposure; risk is the inherent property to cause harm
• Hazard is a chemical’s capacity to cause harm; risk combines hazard with exposure probability to estimate likelihood of harm
• Hazard and risk are interchangeable terms with identical meaning
• Risk only applies to environmental toxins while hazard applies to pharmaceuticals

Correct Answer: Hazard is a chemical’s capacity to cause harm; risk combines hazard with exposure probability to estimate likelihood of harm

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