Principles of toxicology – definition and types of toxicity MCQs With Answer

Introduction:
The principles of toxicology explain how chemicals produce harmful effects, covering definition of toxicity, dose-response relationships, and types of toxicity such as acute, subacute, subchronic and chronic toxicity. Key concepts for B.Pharm students include toxicokinetics (ADME), toxicodynamics, LD50, NOAEL/LOAEL, therapeutic index, bioaccumulation, organ-specific toxicity (hepatotoxicity, nephrotoxicity, neurotoxicity), metabolism (Phase I/II), and interactions like synergism or antagonism. Understanding hazard versus risk, routes of exposure, and regulatory endpoints is essential for drug safety assessment and risk management. Clear grasp of these topics prepares you for clinical and regulatory roles. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What is the best definition of toxicology?

• Study of the beneficial effects of chemicals on organisms
• Study of the adverse effects of chemicals on living organisms
• Study of drug efficacy and therapeutic outcomes
• Study of nutritional requirements and deficiencies

Correct Answer: Study of the adverse effects of chemicals on living organisms

Q2. Which grouping correctly lists common types of toxicity by exposure duration?

• Acute, subacute, subchronic, chronic
• Primary, secondary, tertiary, quaternary
• Local, systemic, generalized, focal
• Internal, external, combined, isolated

Correct Answer: Acute, subacute, subchronic, chronic

Q3. LD50 refers to which concept in toxicology?

• Lowest dose that causes any effect in humans
• Dose that produces therapeutic effect in 50% of patients
• Dose causing death in 50% of a test population
• Lowest observed adverse effect level

Correct Answer: Dose causing death in 50% of a test population

Q4. NOAEL stands for which of the following?

• No Observed Adverse Effect Level
• Normal Observed Acute Exposure Limit
• Net Observable Average Effect Level
• Non-Operative Absorption Exposure Limit

Correct Answer: No Observed Adverse Effect Level

Q5. Which are the principal routes of exposure relevant to toxicology?

• Inhalation, oral (ingestion), dermal, parenteral
• Transdermal only
• Subcutaneous only
• Rectal only

Correct Answer: Inhalation, oral (ingestion), dermal, parenteral

Q6. The dose–response relationship primarily indicates:

• That response occurs identically regardless of dose
• That biological response increases with increasing dose
• That only low doses produce effects
• That time of exposure is irrelevant

Correct Answer: That biological response increases with increasing dose

Q7. The therapeutic index is commonly defined as:

• ED50/TD50
• TD50/ED50
• LD50 × ED50
• NOAEL/LOAEL

Correct Answer: TD50/ED50

Q8. Bioaccumulation refers to:

• Decrease of chemical concentration in an organism over time
• Gradual accumulation of a chemical in an organism over time
• Increase of chemical toxicity due to heat
• Metabolism of xenobiotics to non-toxic products

Correct Answer: Gradual accumulation of a chemical in an organism over time

Q9. Which drug is a classic example of dose-dependent hepatotoxicity?

• Aspirin at analgesic doses
• Paracetamol (acetaminophen) in overdose
• Insulin causing liver necrosis
• Propranolol causing hepatic steatosis at therapeutic doses

Correct Answer: Paracetamol (acetaminophen) in overdose

Q10. Phase I hepatic metabolism typically involves:

• Conjugation to glucuronides and sulfates only
• Introduction or unmasking of polar functional groups via oxidation, reduction or hydrolysis
• Complete elimination without biotransformation
• Primary excretion via bile without modification

Correct Answer: Introduction or unmasking of polar functional groups via oxidation, reduction or hydrolysis

Q11. Intrinsic toxicity differs from idiosyncratic toxicity in that intrinsic toxicity is:

• Unpredictable and unrelated to dose
• Predictable, dose-dependent and reproducible across species
• Only immune-mediated
• Always chronic in nature

Correct Answer: Predictable, dose-dependent and reproducible across species

Q12. Biomagnification means:

• Decreasing concentration of a pollutant up the food chain
• Increasing concentration of a pollutant up the food chain
• Conversion of pollutants into harmless metabolites
• Removal of pollutants by microbial action

Correct Answer: Increasing concentration of a pollutant up the food chain

Q13. Toxicokinetics is best summarized as the study of:

• How a toxicant causes DNA mutations
• Absorption, distribution, metabolism and excretion of toxicants (ADME)
• Social impact of chemical exposure
• Only the metabolic fate of nutrients

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

Q14. The difference between NOEL and NOAEL is that NOEL refers to:

• No observed effect level (no effect at all), while NOAEL allows non‑adverse effects
• No observed adverse effect level, same as NOAEL
• Lowest dose that causes death
• Maximum tolerated dose in humans

Correct Answer: No observed effect level (no effect at all), while NOAEL allows non‑adverse effects

Q15. Mutagenicity is defined as:

• The ability to induce allergic reactions
• The capacity to cause heritable changes in genetic material (DNA)
• The production of excess enzymes in liver
• The prevention of DNA replication

Correct Answer: The capacity to cause heritable changes in genetic material (DNA)

Q16. Teratogenicity describes a toxic effect that:

• Causes cancer in adults only
• Produces developmental malformations in the embryo or fetus
• Enhances fertility and reproduction
• Only affects the immune system

Correct Answer: Produces developmental malformations in the embryo or fetus

Q17. The regulatory “gold standard” for assessing chronic carcinogenic potential is:

• Short-term in vitro bacterial mutation test only
• Long-term two‑year rodent bioassay
• Single-dose acute toxicity test
• Skin sensitization assay in rabbits

Correct Answer: Long-term two‑year rodent bioassay

Q18. Hormesis in toxicology refers to:

• A linear increase in toxicity with dose
• A biphasic dose response where low doses stimulate and high doses inhibit
• Irreversible toxicity at all doses
• Only nutritional benefits from toxins

Correct Answer: A biphasic dose response where low doses stimulate and high doses inhibit

Q19. Which statement best describes a synergistic interaction between two chemicals?

• The combined effect equals the sum of individual effects
• The combined effect is less than the effect of the most potent alone
• The combined effect is greater than the sum of the individual effects
• They neutralize each other completely

Correct Answer: The combined effect is greater than the sum of the individual effects

Q20. Organophosphate pesticides cause toxicity mainly by:

• Inhibiting cytochrome P450 enzymes
• Inhibiting acetylcholinesterase, causing cholinergic overstimulation
• Blocking sodium channels in muscle
• Inducing allergic dermatitis only

Correct Answer: Inhibiting acetylcholinesterase, causing cholinergic overstimulation

Q21. Biomarkers of exposure differ from biomarkers of effect by indicating:

• Physiological response without evidence of exposure
• Exposure to the chemical or its metabolite rather than a biological response
• Only genetic predisposition to disease
• Environmental concentration without biological relevance

Correct Answer: Exposure to the chemical or its metabolite rather than a biological response

Q22. A lower LD50 value implies that a substance is:

• Less toxic
• More toxic
• Not toxic at all
• Only toxic after chronic exposure

Correct Answer: More toxic

Q23. An uncertainty (safety) factor is used to:

• Increase the acceptable daily intake above NOAEL
• Derive a safe exposure level (ADI) from NOAEL by accounting for interspecies and intraspecies differences
• Eliminate the need for animal testing
• Guarantee zero risk from a chemical

Correct Answer: Derive a safe exposure level (ADI) from NOAEL by accounting for interspecies and intraspecies differences

Q24. Irreversible toxic effects are most commonly associated with:

• Transient enzyme inhibition that rapidly reverses
• Permanent cell death or DNA damage leading to loss of function
• Mild reversible inflammation only
• Temporary sedation

Correct Answer: Permanent cell death or DNA damage leading to loss of function

Q25. Which routes bypass first‑pass hepatic metabolism?

• Oral and rectal
• Intravenous and sublingual
• Gastric and enteric
• Topical on intact skin only

Correct Answer: Intravenous and sublingual

Q26. Idiosyncratic drug reactions are typically characterized by:

• High predictability and direct dose dependence
• Unpredictability, rarity, and often immune or metabolic basis
• Occurrence only in animal models
• Dependence solely on organ accumulation

Correct Answer: Unpredictability, rarity, and often immune or metabolic basis

Q27. Which example best illustrates chronic toxicity?

• Single ingestion of a large dose of cyanide
• Repeated low-level lead exposure causing cognitive decline over years
• Immediate anaphylaxis after a bee sting
• Acute alcohol intoxication

Correct Answer: Repeated low-level lead exposure causing cognitive decline over years

Q28. Toxicodynamics focuses on:

• How the body handles a toxicant (ADME)
• Mechanisms by which a toxicant interacts with molecular targets to produce effects
• Only the environmental distribution of chemicals
• Analytical measurement techniques in the lab

Correct Answer: Mechanisms by which a toxicant interacts with molecular targets to produce effects

Q29. Occupational exposure limits (OELs) are primarily established to:

• Ensure workers are exposed to maximal tolerable doses
• Protect workers from adverse health effects during a working lifetime
• Define the lethal dose for emergency responders
• Determine environmental pollution taxes

Correct Answer: Protect workers from adverse health effects during a working lifetime

Q30. OECD test guidelines are used in toxicology to:

• Provide standardized methods for toxicity testing for regulatory submissions
• Replace all animal tests with human trials
• Set clinical dosing regimens for patients
• Define cosmetic marketing claims

Correct Answer: Provide standardized methods for toxicity testing for regulatory submissions

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com