Factors affecting drug metabolism MCQs With Answer

Understanding the factors affecting drug metabolism is essential for B.Pharm students studying pharmacokinetics and clinical therapeutics. This introduction covers key concepts such as hepatic metabolism, enzyme induction and inhibition, genetic polymorphism of CYP450 enzymes, age-related changes, disease states, drug interactions, first-pass metabolism, plasma protein binding, and the role of transporters like P-gp. Grasping how intrinsic and extrinsic factors alter clearance, bioavailability, and half-life helps predict dosing, adverse effects, and therapeutic outcomes. Emphasis on phase I/II reactions, organ blood flow, and clinical implications prepares students for rational drug therapy and patient safety. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. Which of the following is an intrinsic factor that most directly affects hepatic drug metabolism?

• Age-related changes in enzyme expression
• Concomitant herbal supplements
• Alcohol ingestion
• Grapefruit juice consumption

Correct Answer: Age-related changes in enzyme expression

Q2. Which cytochrome P450 isoenzyme is most commonly involved in clinically significant drug interactions?

• CYP1A2
• CYP2D6
• CYP2C9
• CYP3A4

Correct Answer: CYP3A4

Q3. Enzyme induction typically results in which pharmacokinetic change for affected drugs?

• Increased half-life
• Increased clearance
• Decreased volume of distribution
• Increased bioavailability

Correct Answer: Increased clearance

Q4. Genetic polymorphism of CYP2D6 can lead to which clinical phenotype?

• Ultra-rapid metabolizer
• Hepatic failure metabolizer
• Zero-order metabolizer
• Renal poor excretor

Correct Answer: Ultra-rapid metabolizer

Q5. Which phase II reaction commonly increases water solubility and promotes renal excretion?

• Oxidation by CYP450
• Glucuronidation
• Hydroxylation
• Deamination

Correct Answer: Glucuronidation

Q6. First-pass metabolism primarily affects which pharmacokinetic parameter?

• Half-life
• Bioavailability
• Volume of distribution
• Protein binding

Correct Answer: Bioavailability

Q7. Which extrinsic factor is known to inhibit CYP3A4 and raise plasma levels of co-administered drugs?

• Rifampicin
• Carbamazepine
• Ketoconazole
• Smoking tobacco

Correct Answer: Ketoconazole

Q8. Pregnancy often alters drug metabolism due to which of the following?

• Decreased cardiac output
• Increased plasma albumin concentration
• Changes in hormone levels leading to altered enzyme activity
• Permanent loss of CYP enzymes

Correct Answer: Changes in hormone levels leading to altered enzyme activity

Q9. Which organ blood flow change most strongly affects high-extraction-ratio drugs?

• Renal blood flow
• Hepatic blood flow
• Pulmonary blood flow
• Splanchnic venous return

Correct Answer: Hepatic blood flow

Q10. Plasma protein binding influences drug metabolism by affecting which parameter?

• Fraction unbound available for hepatic clearance
• Renal secretion rate only
• CYP enzyme expression levels
• Gastric absorption pH

Correct Answer: Fraction unbound available for hepatic clearance

Q11. Smoking induces which CYP enzyme, often reducing plasma concentrations of substrates?

• CYP3A4
• CYP1A2
• CYP2C19
• CYP2E1

Correct Answer: CYP1A2

Q12. Which metabolic pathway is primarily involved in acetaminophen toxicity at high doses?

• Glucuronidation
• Sulfation
• Formation of a reactive metabolite via CYP (NAPQI)
• Direct renal conjugation

Correct Answer: Formation of a reactive metabolite via CYP (NAPQI)

Q13. Which transporter is most associated with limiting oral absorption and promoting drug efflux from enterocytes?

• OAT1
• PEPT1
• P-glycoprotein (P-gp)
• GLUT2

Correct Answer: P-glycoprotein (P-gp)

Q14. Reduced hepatic function from cirrhosis typically causes which change in drug handling?

• Decreased bioavailability due to increased first-pass
• Increased clearance for high-extraction drugs
• Decreased clearance and prolonged half-life
• Enhanced glucuronidation capacity

Correct Answer: Decreased clearance and prolonged half-life

Q15. Which dietary component is notorious for inhibiting intestinal CYP3A4 and altering drug metabolism?

• Cruciferous vegetables
• Grapefruit juice
• Leafy greens
• High-fiber cereals

Correct Answer: Grapefruit juice

Q16. In neonates, which factor primarily reduces drug metabolism compared to adults?

• Increased CYP enzyme activity
• Immature hepatic enzyme systems
• Faster renal clearance
• Enhanced plasma protein binding

Correct Answer: Immature hepatic enzyme systems

Q17. Which enzyme polymorphism affects metabolism of thiopurines and requires dose adjustments?

• N-acetyltransferase (NAT)
• Thiopurine methyltransferase (TPMT)
• UDP-glucuronosyltransferase (UGT1A1)
• CYP2C9

Correct Answer: Thiopurine methyltransferase (TPMT)

Q18. Enterohepatic recirculation affects drug levels by which mechanism?

• Preventing biliary excretion entirely
• Causing repeated absorption cycles and prolonging exposure
• Increasing renal elimination
• Reducing oral bioavailability permanently

Correct Answer: Causing repeated absorption cycles and prolonging exposure

Q19. Which factor can convert a low-extraction drug into one with clinically significant first-pass loss?

• Severe reduction in hepatic blood flow
• Concurrent strong enzyme induction
• High plasma protein binding
• Change in gastric pH alone

Correct Answer: Concurrent strong enzyme induction

Q20. Which laboratory measure best reflects hepatic metabolic capacity for drug clearance?

• Serum creatinine
• Liver biopsy histology alone
• Serum albumin concentration
• Observational measures of drug clearance (e.g., clearance or intrinsic clearance)

Correct Answer: Observational measures of drug clearance (e.g., clearance or intrinsic clearance)

Q21. Co-administration of a CYP inhibitor with a prodrug activated by the same CYP will likely cause what effect?

• Increased active metabolite concentration
• Decreased conversion to the active drug and reduced efficacy
• No change to therapeutic effect
• Faster onset of action

Correct Answer: Decreased conversion to the active drug and reduced efficacy

Q22. Which factor is most likely to alter drug metabolism during chronic alcohol use?

• Inhibition of CYP2E1 only
• Induction of certain CYP enzymes like CYP2E1
• Permanent loss of phase II enzymes
• Immediate decrease in hepatic blood flow

Correct Answer: Induction of certain CYP enzymes like CYP2E1

Q23. Which pH-dependent change in urine can influence renal elimination and indirectly affect overall drug exposure?

• Urine alkalinization increases elimination of weak bases
• Urine acidification increases elimination of weak acids
• Urine alkalinization increases elimination of weak acids
• Urine pH has no effect on renal elimination

Correct Answer: Urine alkalinization increases elimination of weak acids

Q24. A drug primarily metabolized by UGT enzymes is most likely to undergo which reaction?

• Glucuronidation (phase II conjugation)
• N-demethylation (phase I)
• Sulfation (phase II)
• Oxidative deamination

Correct Answer: Glucuronidation (phase II conjugation)

Q25. Which clinical scenario most increases risk of drug–drug interaction via competitive inhibition at CYP active sites?

• Co-administration of two drugs both metabolized by the same CYP enzyme
• Drugs eliminated exclusively by renal filtration
• Drugs with dissimilar protein binding
• Combining a drug with a dietary supplement that has no effect on CYP

Correct Answer: Co-administration of two drugs both metabolized by the same CYP enzyme

Q26. Which statement about age-related changes in drug metabolism is correct?

• Children always have slower metabolism than adults
• Elderly patients often have reduced hepatic clearance due to decreased liver mass and blood flow
• Metabolic enzyme activity is identical across all ages
• Neonates metabolize drugs faster than adolescents

Correct Answer: Elderly patients often have reduced hepatic clearance due to decreased liver mass and blood flow

Q27. Which pharmacokinetic parameter is directly proportional to hepatic clearance for flow-limited drugs?

• Intrinsic clearance only
• Fraction unbound only
• Hepatic blood flow
• Volume of distribution

Correct Answer: Hepatic blood flow

Q28. Which drug interaction mechanism involves displacement from plasma proteins and subsequent increase in free drug concentration?

• Enzyme induction
• Transporter inhibition
• Protein binding displacement
• First-pass metabolism enhancement

Correct Answer: Protein binding displacement

Q29. Poor metabolizers for CYP2C19 would be expected to show which effect with a drug inactivated by CYP2C19?

• Decreased plasma concentrations and therapeutic failure
• Increased plasma concentrations and potential toxicity
• No change because CYP2C19 is irrelevant
• Faster onset and offset of drug action

Correct Answer: Increased plasma concentrations and potential toxicity

Q30. Which clinical action is most appropriate when a patient starts a potent CYP inhibitor while taking a drug with a narrow therapeutic index?

• No change needed
• Increase the dose of the narrow therapeutic index drug
• Monitor drug levels and consider dose reduction
• Switch to an unrelated over-the-counter supplement

Correct Answer: Monitor drug levels and consider dose reduction

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