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Question 1. Which of the following best defines LD₅₀ in toxicology? A) Lethal dose for 50% of the population B) Lowest dose causing observable effects C) Dose required for therapeutic effect in 50% D) Dose leading to chronic toxicity Answer: A Explanation: LD₅₀ is the dose at which 50% of the test population is expected to die, a standard measure of acute toxicity. Question 2. What is the primary function of Phase II metabolism? A) Increase lipophilicity B) Decrease water solubility C) Conjugate compounds for excretion D) Activate prodrugs Answer: C Explanation: Phase II reactions conjugate drugs with molecules like glucuronic acid, increasing water solubility and facilitating excretion. Question 3. Which organ is most commonly associated with drug-induced hepatotoxicity? A) Kidney B) Liver C) Heart D) Brain Answer: B Explanation: The liver is the main organ for drug metabolism and is highly susceptible to toxic injury.
Question 4. Which term refers to the ability of a chemical to cause permanent damage after repeated exposure over months? A) Acute toxicity B) Subacute toxicity C) Chronic toxicity D) Subchronic toxicity Answer: C Explanation: Chronic toxicity is damage resulting from long-term, repeated exposures. Question 5. What does the therapeutic index (TI) measure? A) Drug efficacy B) Drug potency C) Safety margin D) Rate of absorption Answer: C Explanation: TI compares the toxic dose to the therapeutic dose, indicating the drug’s safety margin. Question 6. Which analytical technique separates compounds based on their interactions with a stationary and mobile phase? A) Spectroscopy B) Chromatography C) Immunoassay D) Centrifugation Answer: B Explanation: Chromatography is used for separating mixtures through interactions with stationary and mobile phases.
Question 10. Which property affects blood-brain barrier penetration of drugs? A) Molecular size and lipophilicity B) Water solubility C) Protein binding D) pKa alone Answer: A Explanation: The blood-brain barrier favors small, lipophilic compounds for penetration. Question 11. What is the main enzyme family responsible for Phase I oxidative metabolism? A) Cytochrome P B) Glucuronosyl transferase C) Acetyl-CoA carboxylase D) Monoamine oxidase Answer: A Explanation: Cytochrome P450 enzymes carry out most Phase I oxidation reactions. Question 12. Which type of toxicity is assessed after a single exposure? A) Chronic toxicity B) Acute toxicity C) Subchronic toxicity D) Delayed toxicity Answer: B Explanation: Acute toxicity is measured after a single exposure to a substance.
Question 13. Which analytical method is most suitable for quantifying trace levels of drugs in plasma? A) Mass spectrometry B) UV/Vis spectroscopy C) Thin-layer chromatography D) Centrifugation Answer: A Explanation: Mass spectrometry offers high sensitivity for trace quantitation in biological samples. Question 14. What does the term ‘bioavailability’ describe? A) Rate of elimination B) Fraction of administered drug reaching systemic circulation C) Amount of drug metabolized D) Drug’s ability to cause toxicity Answer: B Explanation: Bioavailability is the fraction of an administered dose that reaches the bloodstream. Question 15. Which mechanism is NOT a typical cause of cellular injury by toxins? A) Receptor binding B) Enzyme inhibition C) DNA repair D) Covalent binding Answer: C Explanation: DNA repair is a protective mechanism, not a cause of injury; the others are toxic mechanisms.
A) Separation of nonpolar compounds B) Increased volatility C) Detection of metals D) Direct analysis of gases Answer: A Explanation: Reversed-phase HPLC is ideal for separating nonpolar to moderately polar compounds. Question 20. Which process describes the removal of a drug from the body? A) Absorption B) Distribution C) Metabolism D) Elimination Answer: D Explanation: Elimination encompasses all processes removing a drug, including metabolism and excretion. Question 21. What is the main purpose of derivatization in gas chromatography? A) Increase volatility and detectability B) Reduce toxicity C) Lower melting point D) Increase protein binding Answer: A Explanation: Derivatization enhances volatility and detection of analytes in GC. Question 22. Which mass analyzer is best suited for high-resolution mass analysis?
A) Quadrupole B) Ion trap C) Time-of-flight (TOF) D) Flame ionization detector Answer: C Explanation: TOF analyzers provide high-resolution, accurate mass measurements. Question 23. What is the principle behind ELISA immunoassays? A) Color change upon binding B) Radioactive labeling C) Enzyme-linked antibody detection D) Direct fluorescence Answer: C Explanation: ELISA uses enzyme-linked antibodies to produce a measurable signal. Question 24. Which specimen type is most susceptible to adulteration in drug testing? A) Hair B) Blood C) Oral fluid D) Urine Answer: D Explanation: Urine can be easily adulterated or substituted, requiring integrity checks. Question 25. Which toxicological term refers to the dose at which a drug produces its desired effect in 50% of the population?
B) Low creatinine C) High pH D) High protein Answer: B Explanation: Low creatinine levels suggest urine dilution. Question 29. Which property enhances a drug’s renal excretion? A) Lipophilicity B) Protein binding C) Water solubility D) Large molecular size Answer: C Explanation: Water-soluble drugs are more readily excreted via the kidneys. Question 30. What does the Westgard rule 2-2s indicate in QC? A) Systematic error B) Random error C) Both controls outside 2 SD D) One control outside 1 SD Answer: C Explanation: 2-2s means two consecutive controls exceed 2 standard deviations, indicating a systematic error. Question 31. Which type of chain of custody documentation is critical for forensic specimens? A) Storage temperature log
B) Signature and date for each handler C) Volume of specimen D) Instrument calibration Answer: B Explanation: Chain of custody requires signatures and dates for all specimen handling to ensure integrity. Question 32. What is the main route for lead toxicity in children? A) Dermal absorption B) Inhalation C) Oral ingestion D) Ocular exposure Answer: C Explanation: Children are primarily exposed to lead through ingestion of contaminated dust or paint. Question 33. What is the preferred biological matrix for detecting recent cocaine use? A) Hair B) Urine C) Blood D) Sweat Answer: C Explanation: Blood is best for detecting recent use due to rapid metabolism and elimination. Question 34. Which toxicological principle assesses the likelihood of harm under real-world conditions? A) Hazard identification
B) Phenytoin C) Lithium D) Digoxin Answer: B Explanation: Phenytoin is frequently monitored to maintain therapeutic levels in epilepsy. Question 38. Which concept describes the time required for plasma drug concentration to decrease by half? A) Volume of distribution B) Clearance C) Half-life D) Bioavailability Answer: C Explanation: Half-life is the time needed for the drug concentration to reduce by 50%. Question 39. What is a common sign of opioid withdrawal? A) Hypertension B) Bradycardia C) Diarrhea D) Sedation Answer: C Explanation: Opioid withdrawal often includes diarrhea due to loss of GI motility suppression. Question 40. Which analytical system uses electrospray ionization (ESI) for sample introduction? A) GC-MS
B) LC-MS/MS
C) UV/Vis spectroscopy D) Gel electrophoresis Answer: B Explanation: ESI is a soft ionization technique commonly used in LC-MS/MS. Question 41. Which laboratory control is used to confirm negative results in QC? A) Positive control B) Blank control C) Negative control D) Matrix control Answer: C Explanation: Negative controls confirm the absence of analyte and validate test specificity. Question 42. Which is a common matrix for detecting chronic drug use? A) Blood B) Urine C) Hair D) Saliva Answer: C Explanation: Hair analysis can reveal chronic or past drug use due to slow growth and incorporation. Question 43. Which element is most associated with mercury poisoning? A) Lead B) Arsenic
D) High water solubility Answer: A Explanation: Compounds must absorb UV or visible light for detection in UV/Vis spectroscopy. Question 47. Which toxicological principle is demonstrated when a higher dose causes a greater response? A) Threshold B) Dose-response relationship C) Bioavailability D) Metabolic activation Answer: B Explanation: Dose-response relates the magnitude of effect to the amount of exposure. Question 48. What is the main disadvantage of oral fluid specimens in drug testing? A) Difficult to collect B) Low drug concentration C) Highly invasive D) Not suitable for recent use detection Answer: B Explanation: Oral fluid generally contains lower concentrations of drugs compared to blood or urine. Question 49. Which is NOT a characteristic of zero-order kinetics? A) Constant rate of elimination B) Rate independent of concentration C) Exponential decrease in drug levels
D) Saturable elimination Answer: C Explanation: Zero-order kinetics shows constant elimination regardless of concentration, not exponential decrease. Question 50. Which process in drug metabolism makes compounds more water-soluble for excretion? A) Oxidation B) Conjugation C) Reduction D) Hydrolysis Answer: B Explanation: Conjugation attaches polar groups to drugs, increasing water solubility. Question 51. What is the main role of a detector in chromatography? A) Separate analytes B) Introduce sample C) Measure analyte response D) Adjust mobile phase Answer: C Explanation: The detector measures the response as analytes elute from the column. Question 52. Which is a common cause of false positives in immunoassays? A) Cross-reactivity B) Low specimen volume C) High specificity
D) Methanol/formic acid Answer: A Explanation: The cocaine/benzoylecgonine ratio helps determine time and route of use. Question 56. Which type of calibration uses multiple known concentrations? A) Single-point B) Multi-point C) Internal standard D) External standard Answer: B Explanation: Multi-point calibration uses several standards to ensure accuracy and linearity. Question 57. What is the main risk associated with organophosphate exposure? A) Liver failure B) Cholinesterase inhibition C) Kidney stones D) DNA damage Answer: B Explanation: Organophosphates inhibit cholinesterase enzymes, causing neurotoxicity. Question 58. Which property influences a drug’s ability to cross cell membranes? A) Water solubility B) Lipophilicity C) Protein binding D) Large molecular size
Answer: B Explanation: Lipophilic drugs cross cell membranes more easily than hydrophilic ones. Question 59. What is the main advantage of hair specimens in forensic toxicology? A) Detects acute poisoning B) Reveals long-term drug use C) Low cost D) Easy to adulterate Answer: B Explanation: Hair testing provides a historical record of drug exposure. Question 60. What is the key difference between hazard and risk? A) Hazard is potential harm, risk is likelihood of harm B) Hazard is exposure, risk is effect C) Hazard is dose, risk is response D) Hazard is acute, risk is chronic Answer: A Explanation: Hazard is the inherent potential for harm, while risk considers exposure and likelihood. Question 61. Which is NOT a specimen integrity check for urine? A) Temperature B) Creatinine C) Protein D) Specific gravity Answer: C
