GIT Drug Absorption Mechanisms MCQs With Answer

GIT Drug Absorption Mechanisms MCQs With Answer

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Introduction: This quiz set on GIT Drug Absorption Mechanisms is designed for M.Pharm students studying Advanced Biopharmaceutics & Pharmacokinetics (MIP 201T). It consolidates core concepts such as transcellular and paracellular transport, pH-partition theory, carrier-mediated uptake, enzymatic degradation, efflux transporters, and formulation factors that influence oral absorption. Each question probes mechanistic understanding and practical implications—dissolution, permeability, absorption windows, food effects, and first-pass processes—preparing students for examinations and formulation design decisions. Use these 20 MCQs to test, revise, and deepen your grasp of gastrointestinal absorption principles relevant to drug development and clinical performance.

Q1. Which of the following best describes the primary mechanisms by which drugs traverse the gastrointestinal epithelium?

  • Passive transcellular diffusion, paracellular diffusion, carrier-mediated transport, and endocytosis
  • Only passive transcellular diffusion
  • Only active transporters
  • Only micelle-mediated transport

Correct Answer: Passive transcellular diffusion, paracellular diffusion, carrier-mediated transport, and endocytosis

Q2. According to the pH-partition hypothesis, which property most directly determines the fraction of drug in the unionized form at a given GI pH?

  • Drug pKa (acid dissociation constant)
  • Lipid solubility (log P)
  • Molecular weight
  • Presence of efflux transporters

Correct Answer: Drug pKa (acid dissociation constant)

Q3. Transcellular passive diffusion across enterocytes is primarily driven by which drug characteristics?

  • High lipophilicity and predominance of the unionized species
  • Large molecular size and high charge
  • Affinity for P-glycoprotein efflux
  • Strong binding to bile salts

Correct Answer: High lipophilicity and predominance of the unionized species

Q4. Paracellular transport through tight junctions in the intestine most readily allows absorption of which type of molecules?

  • Small hydrophilic molecules and ions
  • Large lipophilic macromolecules
  • Peptides requiring carrier-mediated uptake
  • Lipoprotein-bound lipids

Correct Answer: Small hydrophilic molecules and ions

Q5. Which transporter is a well-known example of carrier-mediated uptake in the small intestine for di- and tri-peptides?

  • PEPT1 (peptide transporter 1)
  • P-glycoprotein (P-gp)
  • CYP3A4 enzyme
  • OAT1 (organic anion transporter 1)

Correct Answer: PEPT1 (peptide transporter 1)

Q6. Which intestinal membrane protein is most commonly associated with efflux that decreases oral bioavailability of certain drugs?

  • P-glycoprotein (P-gp)
  • PEPT1
  • SGLT1 (sodium-glucose cotransporter)
  • Monocarboxylate transporter (MCT)

Correct Answer: P-glycoprotein (P-gp)

Q7. Large peptide and protein drugs administered orally often show poor absorption primarily because of which mechanism?

  • Proteolytic degradation by luminal and brush-border enzymes
  • Rapid hepatic CYP-mediated metabolism only
  • Excessive passive transcellular diffusion
  • Strong micellar solubilization by bile salts

Correct Answer: Proteolytic degradation by luminal and brush-border enzymes

Q8. Pre-systemic (first-pass) metabolism of orally administered drugs predominantly occurs in which tissues?

  • Intestinal mucosa and liver
  • Stomach only
  • Colon only
  • Systemic circulation before reaching liver

Correct Answer: Intestinal mucosa and liver

Q9. Which condition in the stomach increases absorption of a weak acid drug according to pH-dependent ionization principles?

  • Low gastric pH increasing the unionized fraction of the weak acid
  • High gastric pH increasing the unionized fraction of the weak acid
  • Presence of P-gp efflux transporters
  • Increased bile salt concentration

Correct Answer: Low gastric pH increasing the unionized fraction of the weak acid

Q10. In the Biopharmaceutics Classification System (BCS), which combination predicts highest likelihood of good oral absorption and bioavailability?

  • High aqueous solubility and high intestinal permeability
  • Low solubility and high permeability
  • High solubility and low permeability
  • Low solubility and low permeability

Correct Answer: High aqueous solubility and high intestinal permeability

Q11. For a poorly soluble drug, which step is most often rate-limiting for oral absorption?

  • Dissolution of the drug in gastrointestinal fluids
  • Passive diffusion across cell membranes
  • Renal elimination
  • Protein binding in plasma

Correct Answer: Dissolution of the drug in gastrointestinal fluids

Q12. Delayed gastric emptying is expected to produce which effect on the oral absorption profile of a drug primarily absorbed in the small intestine?

  • Prolonged gastric residence and delayed Tmax for that drug
  • Immediate increase in Cmax for all drugs
  • Complete prevention of absorption
  • No impact on absorption kinetics

Correct Answer: Prolonged gastric residence and delayed Tmax for that drug

Q13. Which of the following drugs is classically cited as having a narrow “absorption window” in the upper small intestine?

  • Levodopa
  • Diazepam
  • Metformin
  • Warfarin

Correct Answer: Levodopa

Q14. A high-fat meal typically affects oral absorption by which principal mechanism for lipophilic drugs?

  • Increasing solubilization via bile-stimulated micelle formation and often increasing bioavailability
  • Always decreasing absorption by delaying gastric emptying only
  • Causing immediate drug degradation by acids
  • Blocking intestinal transporters completely

Correct Answer: Increasing solubilization via bile-stimulated micelle formation and often increasing bioavailability

Q15. Bile salts in the intestinal lumen primarily enhance oral absorption of lipophilic drugs by which mechanism?

  • Forming mixed micelles that increase apparent solubility of lipophilic drugs
  • Direct enzymatic cleavage of the drug
  • Inducing P-gp expression
  • Lowering intestinal pH dramatically

Correct Answer: Forming mixed micelles that increase apparent solubility of lipophilic drugs

Q16. In compartmental pharmacokinetics, which parameter specifically denotes the first-order absorption rate constant?

  • Ka (absorption rate constant)
  • Kd (dissociation constant)
  • Vd (volume of distribution)
  • CL (clearance)

Correct Answer: Ka (absorption rate constant)

Q17. The Caco-2 cell monolayer is widely used in drug development to assess which property relevant to oral absorption?

  • Intestinal epithelial permeability and transporter interactions
  • Hepatic metabolic clearance
  • Renal secretion rates
  • Plasma protein binding

Correct Answer: Intestinal epithelial permeability and transporter interactions

Q18. Reducing particle size of a poorly soluble oral drug (micronization/nanonization) most commonly results in which outcome?

  • Increased dissolution rate and often enhanced absorption
  • Decreased membrane permeability
  • Increased first-pass hepatic metabolism
  • Reduced aqueous solubility

Correct Answer: Increased dissolution rate and often enhanced absorption

Q19. Which enzyme located in enterocytes significantly contributes to pre-systemic metabolism and can limit oral bioavailability of substrates?

  • Intestinal CYP3A4
  • Lipase in the lumen
  • Brush-border alkaline phosphatase only
  • Renal CYP enzymes

Correct Answer: Intestinal CYP3A4

Q20. Facilitated diffusion across the intestinal epithelium is best described by which statement?

  • Carrier-mediated transport down a concentration gradient that is saturable and does not require metabolic energy
  • Active transport requiring ATP to move drug against a gradient
  • Simple passive diffusion proportional to log P
  • Endocytic uptake of large macromolecules

Correct Answer: Carrier-mediated transport down a concentration gradient that is saturable and does not require metabolic energy

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