Renal excretion of drugs and renal clearance MCQs With Answer

Introduction: Renal excretion of drugs and renal clearance are central topics in pharmacokinetics for B.Pharm students. Understanding glomerular filtration, tubular secretion, and tubular reabsorption explains how drugs and metabolites are removed by the kidney. Key concepts include renal clearance calculations, creatinine clearance as a GFR estimator, renal plasma flow, transporter-mediated secretion (OAT/OCT), urine pH effects, and dose adjustments in renal impairment. Mastery of these principles aids rational dosing, predicting drug interactions (e.g., probenecid), and interpreting lab tests. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What are the three primary processes that comprise renal excretion of drugs?

• Metabolic conjugation, biliary secretion, and enterohepatic recycling
• Glomerular filtration, tubular secretion, and tubular reabsorption
• Passive diffusion, facilitated diffusion, and active transport
• First-pass metabolism, distribution, and elimination

Correct Answer: Glomerular filtration, tubular secretion, and tubular reabsorption

Q2. Renal clearance (Clr) of a drug is defined by which equation?

• Clr = (Urine concentration × Urine flow rate) / Plasma concentration
• Clr = (Plasma concentration × Urine flow rate) / Urine concentration
• Clr = Volume of distribution / Elimination rate constant
• Clr = Half-life × Elimination rate constant

Correct Answer: Clr = (Urine concentration × Urine flow rate) / Plasma concentration

Q3. If a drug is highly protein bound in plasma, how is its glomerular filtration affected?

• Filtration is increased because bound drug is filtered preferentially
• Filtration is unchanged because protein binding has no effect
• Filtration is reduced because only unbound drug is filtered
• Filtration becomes active instead of passive

Correct Answer: Filtration is reduced because only unbound drug is filtered

Q4. Which compound is considered the gold standard for measuring true GFR experimentally?

• Creatinine
• Inulin
• Para-aminohippurate (PAH)
• Urea

Correct Answer: Inulin

Q5. PAH (para-aminohippurate) clearance is used to estimate which renal parameter?

• Glomerular filtration rate (GFR)
• Renal plasma flow (RPF)
• Renal threshold for glucose
• Urine osmolality

Correct Answer: Renal plasma flow (RPF)

Q6. A drug with renal clearance greater than GFR likely undergoes which additional process?

• Extensive tubular reabsorption
• Hepatic metabolism only
• Tubular secretion in addition to filtration
• No renal handling at all

Correct Answer: Tubular secretion in addition to filtration

Q7. Which transporter family is primarily responsible for organic anion secretion in renal proximal tubules?

• ATP-binding cassette (ABC) efflux pumps
• Organic cation transporters (OCT)
• Organic anion transporters (OAT)
• Glucose transporters (GLUT)

Correct Answer: Organic anion transporters (OAT)

Q8. Probenecid increases plasma levels of some penicillins by which mechanism?

• Inducing hepatic drug-metabolizing enzymes
• Inhibiting tubular secretion via OAT, reducing renal clearance
• Enhancing glomerular filtration
• Increasing tubular reabsorption of penicillins

Correct Answer: Inhibiting tubular secretion via OAT, reducing renal clearance

Q9. Changing urine pH can alter renal excretion of weak acids and bases by:

• Changing drug protein binding in plasma
• Shifting drug ionization and promoting ion trapping in urine
• Altering GFR directly
• Blocking tubular transporters

Correct Answer: Shifting drug ionization and promoting ion trapping in urine

Q10. Which parameter best describes the fraction of drug removed from plasma by the kidneys per unit time?

• Volume of distribution (Vd)
• Renal clearance (Clr)
• Bioavailability (F)
• Absorption rate constant (Ka)

Correct Answer: Renal clearance (Clr)

Q11. Creatinine clearance slightly overestimates true GFR because:

• Creatinine is reabsorbed in tubules
• Creatinine is secreted by proximal tubules
• Creatinine binds extensively to plasma proteins
• Creatinine is metabolized in the liver

Correct Answer: Creatinine is secreted by proximal tubules

Q12. Fractional excretion of sodium (FENa) is useful clinically to differentiate:

• Hepatic from renal causes of hyponatremia
• Intrinsic renal failure from prerenal azotemia
• Metabolic from respiratory acidosis
• Acute from chronic pancreatitis

Correct Answer: Intrinsic renal failure from prerenal azotemia

Q13. A drug with Clr approximately equal to GFR is most likely:

• Exclusively secreted
• Freely filtered and neither secreted nor reabsorbed
• Extensively reabsorbed
• Metabolized in kidneys

Correct Answer: Freely filtered and neither secreted nor reabsorbed

Q14. Tubular maximum (Tm) is important for which renal phenomenon affecting drugs?

• Saturation of active reabsorption or secretion transporters
• Unlimited passive diffusion across membranes
• Protein binding in plasma
• Filtration of only protein-bound drug

Correct Answer: Saturation of active reabsorption or secretion transporters

Q15. In chronic renal failure, dosing of renally excreted drugs should be adjusted because:

• Renal clearance is increased
• Drug bioavailability is always decreased
• Accumulation leads to toxicity due to reduced clearance
• Volume of distribution always falls to zero

Correct Answer: Accumulation leads to toxicity due to reduced clearance

Q16. Ion trapping enhances urinary excretion of a weak base by making urine more:

• Acidic
• Alkaline
• Isotonic
• Protein-rich

Correct Answer: Acidic

Q17. Which statement about renal clearance units is correct?

• Clr is measured in mg/kg
• Clr is expressed as mL/min or L/hr
• Clr is dimensionless
• Clr is expressed as moles per liter

Correct Answer: Clr is expressed as mL/min or L/hr

Q18. Which clinical test provides the best practical estimate of GFR in routine practice?

• Inulin clearance measured in all patients
• Serum creatinine-based creatinine clearance or estimated GFR equations
• Urine glucose measurement
• 24-hour urine protein only

Correct Answer: Serum creatinine-based creatinine clearance or estimated GFR equations

Q19. A drug with high lipophilicity is likely to undergo which renal process to a greater extent?

• Increased tubular reabsorption leading to decreased urinary excretion
• Increased filtration due to binding to plasma proteins
• Active tubular secretion via OAT
• Immediate renal metabolism

Correct Answer: Increased tubular reabsorption leading to decreased urinary excretion

Q20. Which factor does NOT significantly influence renal excretion of drugs?

• Urine pH
• Plasma protein binding
• Drug molecular size and polarity
• Atmospheric pressure

Correct Answer: Atmospheric pressure

Q21. During competition for tubular secretion, one drug can decrease clearance of another by:

• Competing for the same renal transporter, reducing secretion
• Increasing GFR dramatically
• Binding to urine proteins
• Changing the drug’s pKa in plasma

Correct Answer: Competing for the same renal transporter, reducing secretion

Q22. In overdose management, urinary alkalinization is used to enhance excretion of which type of drug?

• Weak acids (e.g., phenobarbital)
• Strong bases only
• Highly protein-bound drugs
• Neutral lipophilic drugs

Correct Answer: Weak acids (e.g., phenobarbital)

Q23. Filtration fraction (FF) is defined as:

• GFR divided by renal plasma flow (RPF)
• RPF divided by GFR
• Urine flow rate divided by plasma flow
• Renal clearance divided by volume of distribution

Correct Answer: GFR divided by renal plasma flow (RPF)

Q24. Which change would decrease renal clearance of a drug eliminated mainly by tubular secretion?

• Administration of a competitive inhibitor of the secretion transporter
• Increase in GFR
• Decrease in plasma protein binding leaving more free drug
• Urinary acidification for a weak base

Correct Answer: Administration of a competitive inhibitor of the secretion transporter

Q25. Hemodialysis most effectively removes drugs that are:

• Highly protein-bound and with large Vd
• Low molecular weight, water-soluble, and low protein binding
• Extensively sequestered in fat tissues
• Strongly bound to red blood cells

Correct Answer: Low molecular weight, water-soluble, and low protein binding

Q26. The term “renal clearance greater than renal plasma flow” indicates which situation?

• Measurement or calculation error, because clearance cannot exceed plasma flow
• Complete reabsorption of the drug
• Drug is not filtered at all
• Drug is only metabolized in the liver

Correct Answer: Measurement or calculation error, because clearance cannot exceed plasma flow

Q27. Saturable reabsorption of glucose in the proximal tubule is analogous to which drug-related concept?

• Zero-order kinetics due to transporter saturation
• First-pass metabolism in the liver
• Protein binding equilibrium
• Passive diffusion across membranes

Correct Answer: Zero-order kinetics due to transporter saturation

Q28. Which statement about age-related renal changes is correct for drug dosing?

• GFR generally increases with age, requiring higher doses
• Elderly patients often have reduced GFR and may need dose reduction of renally excreted drugs
• Renal plasma flow is unaffected by aging
• Protein binding always increases with age eliminating need for dose adjustment

Correct Answer: Elderly patients often have reduced GFR and may need dose reduction of renally excreted drugs

Q29. Estimation of creatinine clearance from serum creatinine in a 70-kg adult commonly uses which equation or method in clinical practice?

• Henderson-Hasselbalch equation
• Cockcroft-Gault equation
• Michaelis-Menten equation
• Arrhenius equation

Correct Answer: Cockcroft-Gault equation

Q30. Which best describes the effect of diuretics like furosemide on renal drug excretion?

• They always decrease drug excretion by blocking secretion
• They increase urine flow, which can reduce passive reabsorption and increase excretion of some drugs
• They convert weak acids into weak bases
• They eliminate the need for dose adjustment in renal impairment

Correct Answer: They increase urine flow, which can reduce passive reabsorption and increase excretion of some drugs

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