Introduction: Understanding the factors affecting renal excretion of drugs is essential for B. Pharm students studying pharmacokinetics, dose adjustment, and drug safety. Key concepts include glomerular filtration rate (GFR), tubular secretion and reabsorption, plasma protein binding, drug ionization (pKa), urinary pH, renal blood flow, transporters (OAT, OCT, MATE), and drug–drug interactions. Pathophysiological conditions—age, renal impairment, pregnancy, and dialysis—also alter renal clearance and half-life. Mastery of these factors helps predict elimination, adjust dosing, and avoid toxicity. This focused set of MCQs emphasizes mechanisms, clinical implications, and calculation principles to strengthen your applied knowledge. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which process primarily determines whether a drug is filtered freely at the glomerulus?
- Molecular size and protein binding
- Lipid solubility
- Hepatic metabolism rate
- Gastrointestinal absorption
Correct Answer: Molecular size and protein binding
Q2. High plasma protein binding of a drug most directly affects renal excretion by:
- Increasing tubular secretion
- Reducing the fraction available for glomerular filtration
- Enhancing passive reabsorption
- Accelerating renal blood flow
Correct Answer: Reducing the fraction available for glomerular filtration
Q3. Active tubular secretion of organic anions is mediated primarily by which transporter family?
- P-glycoprotein (P-gp)
- OAT (organic anion transporters)
- CYP450 enzymes
- SGLT transporters
Correct Answer: OAT (organic anion transporters)
Q4. Urinary pH most influences renal excretion of drugs by changing:
- Plasma protein binding
- Drug ionization and passive reabsorption
- Glomerular filtration rate
- Active secretion transporter expression
Correct Answer: Drug ionization and passive reabsorption
Q5. Which drug would be more readily excreted in acidic urine: a weak base with pKa 9 or a weak acid with pKa 4?
- The weak base (pKa 9)
- The weak acid (pKa 4)
- Both equally
- Neither; urinary pH has no effect
Correct Answer: The weak base (pKa 9)
Q6. Probenecid increases plasma concentration of penicillin by:
- Inducing renal transporters
- Competing for tubular secretion, reducing renal excretion
- Enhancing glomerular filtration
- Increasing hepatic metabolism
Correct Answer: Competing for tubular secretion, reducing renal excretion
Q7. A decrease in renal blood flow will most likely cause:
- Increased glomerular filtration of drugs
- Reduced renal clearance for flow-dependent drugs
- Enhanced tubular secretion
- No change in drug elimination
Correct Answer: Reduced renal clearance for flow-dependent drugs
Q8. Which statement correctly distinguishes tubular secretion from passive reabsorption?
- Tubular secretion is energy-independent; passive reabsorption requires ATP
- Tubular secretion is carrier-mediated and can be saturated; passive reabsorption depends on concentration gradients and lipophilicity
- Both are identical and interchangeable
- Passive reabsorption only occurs for polar drugs
Correct Answer: Tubular secretion is carrier-mediated and can be saturated; passive reabsorption depends on concentration gradients and lipophilicity
Q9. In chronic renal failure, which pharmacokinetic parameter commonly increases for renally cleared drugs?
- Renal clearance
- Elimination half-life
- Glomerular filtration fraction
- Hepatic clearance
Correct Answer: Elimination half-life
Q10. Which factor would enhance passive reabsorption of a drug from renal tubules back into blood?
- High ionization at tubular pH
- High lipid solubility and non-ionized form in tubular fluid
- Strong binding to tubular proteins
- Low membrane permeability
Correct Answer: High lipid solubility and non-ionized form in tubular fluid
Q11. Which clinical condition is most likely to reduce glomerular filtration rate (GFR) and thus decrease renal excretion?
- Hypervolemia
- Acute tubular necrosis
- Pregnancy in third trimester
- Enhanced renal perfusion
Correct Answer: Acute tubular necrosis
Q12. Renal clearance of a drug equals glomerular filtration only when:
- The drug is highly protein-bound and actively secreted
- There is no tubular secretion or reabsorption and the drug is freely filtered
- Urinary pH is extremely acidic
- The drug is lipophilic and extensively reabsorbed
Correct Answer: There is no tubular secretion or reabsorption and the drug is freely filtered
Q13. Which drug property increases likelihood of active tubular secretion?
- Being a large hydrophobic molecule (>500 Da)
- Being an organic anion or cation recognized by renal transporters
- Extreme lipophilicity causing rapid passive diffusion
- High degree of hepatic conjugation only
Correct Answer: Being an organic anion or cation recognized by renal transporters
Q14. Which transporter is primarily involved in secretion of organic cations in renal tubules?
- OAT
- OCT (organic cation transporter)
- Na+/K+ ATPase
- GLUT transporters
Correct Answer: OCT (organic cation transporter)
Q15. Which intervention can be used clinically to increase urinary excretion of a weak acid overdose?
- Alkalinize the urine
- Acidify the urine
- Give a bile sequestrant
- Administer activated charcoal only
Correct Answer: Alkalinize the urine
Q16. A drug with renal clearance greater than GFR likely undergoes:
- Significant tubular secretion
- Complete passive reabsorption
- Only hepatic metabolism
- No renal handling
Correct Answer: Significant tubular secretion
Q17. Which age-related change decreases renal excretion in elderly patients?
- Increased GFR
- Decreased renal blood flow and GFR
- Higher muscle mass increasing creatinine
- Enhanced expression of renal transporters
Correct Answer: Decreased renal blood flow and GFR
Q18. Competitive inhibition at renal transporters can cause:
- Decreased plasma levels of co-administered drugs
- Increased renal excretion of both drugs
- Decreased secretion and increased plasma concentration of one drug
- No change in drug interactions
Correct Answer: Decreased secretion and increased plasma concentration of one drug
Q19. Which statement about dialysis and drug removal is true?
- Highly protein-bound drugs are efficiently removed by dialysis
- Small, water-soluble, low protein-bound drugs are easily dialyzed
- Lipophilic, highly distributed drugs are removed rapidly by dialysis
- Dialysis increases hepatic metabolism of drugs
Correct Answer: Small, water-soluble, low protein-bound drugs are easily dialyzed
Q20. In metabolic acidosis, renal excretion of weak bases is generally:
- Decreased due to increased ionization of bases
- Increased because bases become more non-ionized
- Unaffected by systemic pH changes
- Converted to active metabolites
Correct Answer: Decreased due to increased ionization of bases
Q21. Which laboratory measure is commonly used to estimate renal function for drug dosing?
- Serum bilirubin
- Creatinine clearance or estimated GFR
- Serum amylase
- Liver function tests
Correct Answer: Creatinine clearance or estimated GFR
Q22. A drug that undergoes extensive tubular reabsorption will have which of the following characteristics?
- High urinary excretion unchanged
- Low renal clearance compared to GFR
- Clearance equal to renal plasma flow
- Complete removal by hemodialysis
Correct Answer: Low renal clearance compared to GFR
Q23. Which factor does NOT directly affect renal drug excretion?
- Plasma protein binding
- Urinary flow rate
- Hepatic cytochrome activity
- Drug pKa relative to urine pH
Correct Answer: Hepatic cytochrome activity
Q24. Genetic polymorphism in renal transporters may lead to:
- Uniform drug elimination in all patients
- Inter-individual variability in renal excretion and drug response
- Only changes in hepatic clearance
- No clinical significance
Correct Answer: Inter-individual variability in renal excretion and drug response
Q25. Which pharmacokinetic equation relates clearance, volume of distribution, and half-life?
- t1/2 = 0.693 × Vd / CL
- t1/2 = CL / Vd
- CL = Vd × t1/2
- Vd = CL / t1/2
Correct Answer: t1/2 = 0.693 × Vd / CL
Q26. In the setting of proteinuria, renal excretion of a normally protein-bound drug may:
- Decrease due to binding to urinary proteins only
- Increase because albumin loss raises free drug fraction in plasma
- Remain unchanged since urinary loss has no effect
- Be eliminated solely by hepatic metabolism
Correct Answer: Increase because albumin loss raises free drug fraction in plasma
Q27. Which drug interaction would decrease renal secretion of an organic cation substrate?
- Co-administration with an OAT inhibitor
- Co-administration with an OCT inhibitor
- Administration of a proton pump inhibitor
- Co-administration with activated charcoal
Correct Answer: Co-administration with an OCT inhibitor
Q28. Which characteristic favors renal excretion rather than hepatic metabolism?
- Extremely lipophilic and highly protein-bound drug
- Small, polar, unchanged drug eliminated in urine
- Prodrug requiring hepatic activation
- Drug undergoing extensive biliary excretion
Correct Answer: Small, polar, unchanged drug eliminated in urine
Q29. Which diuretic effect can increase urinary excretion of some drugs by reducing passive reabsorption?
- Decreased urine flow (antidiuretic effect)
- Increased urine flow (diuresis), washing out tubular lumen
- Enhanced protein binding in plasma
- Inhibition of GFR entirely
Correct Answer: Increased urine flow (diuresis), washing out tubular lumen
Q30. A drug has a GFR of 120 mL/min, is 90% protein bound, and has no secretion or reabsorption. What is its approximate renal clearance?
- 120 mL/min
- 12 mL/min
- 108 mL/min
- 0 mL/min
Correct Answer: 12 mL/min
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