Factors influencing drug absorption through GIT MCQs With Answer

Introduction

Understanding the factors influencing drug absorption through the GIT is essential for B.Pharm students. Drug absorption depends on physicochemical properties (solubility, pKa, lipophilicity/log P), formulation factors (particle size, salt form, excipients), physiological variables (gastric pH, gastric emptying, intestinal transit time, surface area, blood flow), and biological barriers (first‑pass metabolism, P‑glycoprotein efflux, intestinal enzymes). Concepts like pH partitioning, dissolution rate (Noyes‑Whitney), lymphatic uptake, and enterohepatic recycling determine bioavailability and therapeutic response. Mastery of these keywords and mechanisms helps in rational formulation and dose optimization. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. Which statement best describes the pH partition hypothesis relevant to GIT absorption?

• Unionized form predominates when drug pH equals pKa
• Weak acids are more unionized at pH greater than pKa
• Weak bases are more unionized at pH above their pKa
• Unionized species cross membranes more readily than ionized species

Correct Answer: Unionized species cross membranes more readily than ionized species

Q2. According to the Noyes‑Whitney equation, which factor most directly increases the dissolution rate of a poorly soluble drug?

• Decreasing diffusion coefficient
• Reducing particle surface area
• Increasing particle size
• Increasing surface area (particle size reduction)

Correct Answer: Increasing surface area (particle size reduction)

Q3. Which organ and enzyme system are primarily responsible for first‑pass hepatic metabolism affecting oral bioavailability?

• Small intestine and monoamine oxidase
• Liver and cytochrome P450 (CYP) enzymes
• Stomach and pepsin
• Colon and bacterial dehydrogenases

Correct Answer: Liver and cytochrome P450 (CYP) enzymes

Q4. P‑glycoprotein (P‑gp) in enterocytes primarily affects oral drug absorption by which mechanism?

• Increasing passive diffusion across the membrane
• Acting as an uptake transporter into blood
• Pumping substrates back into the intestinal lumen (efflux)
• Hydrolyzing drugs in the brush border

Correct Answer: Pumping substrates back into the intestinal lumen (efflux)

Q5. In the Biopharmaceutics Classification System (BCS), a Class I drug is characterized by which properties?

• Low solubility, low permeability
• High solubility, high permeability
• High solubility, low permeability
• Low solubility, high permeability

Correct Answer: High solubility, high permeability

Q6. Which log P (octanol‑water partition coefficient) range is generally considered favorable for passive transcellular absorption across enterocytes?

• Less than −1
• Approximately 1–3
• Greater than 6
• Exactly 0

Correct Answer: Approximately 1–3

Q7. How does a high‑fat meal commonly influence the oral absorption of highly lipophilic drugs?

• Decreases absorption by preventing dissolution
• Increases absorption via bile salt solubilization and lymphatic uptake
• Has no effect on lipophilic drugs
• Accelerates gastric emptying to reduce Tmax

Correct Answer: Increases absorption via bile salt solubilization and lymphatic uptake

Q8. Delayed gastric emptying will most likely cause which change in oral pharmacokinetics?

• Decrease in Tmax (time to peak concentration)
• Immediate increase in absorption rate
• Increase in Tmax and possible change in extent of absorption
• Complete prevention of intestinal absorption

Correct Answer: Increase in Tmax and possible change in extent of absorption

Q9. Bile salts in the small intestine primarily enhance absorption of which type of drugs?

• Hydrophilic small molecules via paracellular route
• Highly lipophilic drugs by micellar solubilization
• Large proteins via transcytosis
• Strong acids by ion pairing

Correct Answer: Highly lipophilic drugs by micellar solubilization

Q10. Which physicochemical property most favors intestinal lymphatic transport?

• Low molecular weight and high water solubility
• High polarity and multiple hydrogen bond donors
• High lipophilicity (very high log P) and long‑chain lipid solubility
• Extensive ionization at intestinal pH

Correct Answer: High lipophilicity (very high log P) and long‑chain lipid solubility

Q11. Which anatomical features of the small intestine most increase oral drug absorption?

• Thick mucus layer and lacking villi
• Lymphoid follicles only
• Large surface area due to villi and microvilli
• Dense keratinized epithelium

Correct Answer: Large surface area due to villi and microvilli

Q12. Where is a weak acid most likely to be predominantly unionized and therefore more membrane‑permeable?

• Small intestine (pH ~7–8)
• Stomach (low pH)
• Colon (neutral pH)
• Blood plasma (pH 7.4)

Correct Answer: Stomach (low pH)

Q13. Which antifungal drug’s oral absorption is notably reduced by acid‑suppressing agents (antacids, PPIs) due to pH‑dependent solubility?

• Fluconazole
• Ketoconazole
• Amphotericin B
• Terbinafine

Correct Answer: Ketoconazole

Q14. Compared to the small intestine, the colon generally shows which characteristic affecting drug absorption?

• Greater surface area and higher permeability
• Lower surface area and fewer transporters, reducing absorption
• Higher enzymatic hydrolysis leading to increased absorption
• More villi and microvilli than small intestine

Correct Answer: Lower surface area and fewer transporters, reducing absorption

Q15. Binding of a drug to intestinal mucin is most likely to cause which effect on oral absorption?

• Increase in the free drug concentration at the epithelium
• Enhanced transcellular diffusion
• Reduced absorption due to sequestration in the mucus layer
• Activation of prodrug to active form

Correct Answer: Reduced absorption due to sequestration in the mucus layer

Q16. Which cytochrome P450 isoform is most abundant in human enterocytes and significantly contributes to gut wall metabolism?

• CYP2D6
• CYP1A2
• CYP3A4
• CYP2E1

Correct Answer: CYP3A4

Q17. Why does micronization (particle size reduction) enhance oral absorption of poorly soluble drugs?

• It decreases the drug’s surface area
• It lowers the solid state energy
• It increases dissolution rate by increasing surface area
• It converts the drug into a salt form

Correct Answer: It increases dissolution rate by increasing surface area

Q18. Converting a weakly basic drug into its hydrochloride salt primarily aims to improve which property?

• Lipophilicity
• Permeability through lipid membranes
• Aqueous solubility
• Resistance to metabolic enzymes

Correct Answer: Aqueous solubility

Q19. Enterohepatic recycling of a drug typically results in which pharmacokinetic feature?

• Reduced plasma half‑life
• Single sharp plasma peak without secondary peaks
• Prolonged presence in plasma and possible secondary peaks
• Immediate renal excretion only

Correct Answer: Prolonged presence in plasma and possible secondary peaks

Q20. Paracellular absorption across intestinal epithelium is most suitable for which type of molecules?

• Large lipophilic molecules transported by transcytosis
• Small hydrophilic molecules restricted by tight junctions
• High molecular weight proteins
• Highly lipophilic drugs with log P > 5

Correct Answer: Small hydrophilic molecules restricted by tight junctions

Q21. Crohn’s disease affecting the ileum is likely to produce which effect on oral drug absorption?

• Enhanced absorption due to increased surface area
• No change in absorption
• Reduced absorption due to inflammation, ulceration, and decreased surface area
• Immediate complete absorption of all drugs

Correct Answer: Reduced absorption due to inflammation, ulceration, and decreased surface area

Q22. In the equation for oral bioavailability F = fa × fg × fh, what does fa represent?

• Fraction escaping hepatic metabolism
• Fraction of dose absorbed across the gut wall into enterocytes
• Fraction undergoing renal excretion unchanged
• Fraction metabolized by gut enzymes

Correct Answer: Fraction of dose absorbed across the gut wall into enterocytes

Q23. Organic anion‑transporting polypeptides (OATPs) in the intestine typically play what role in drug absorption?

• Efflux of drugs back to lumen
• Passive diffusion across membranes
• Carrier‑mediated uptake of substrates into enterocytes
• Covalent modification of drugs

Correct Answer: Carrier‑mediated uptake of substrates into enterocytes

Q24. The unstirred water layer or microclimate near the enterocyte surface mainly affects absorption by altering which parameter?

• Drug hepatic clearance
• Local pH and diffusion resistance affecting ionization and diffusion
• Systemic distribution volume
• Renal filtration rate

Correct Answer: Local pH and diffusion resistance affecting ionization and diffusion

Q25. Mucoadhesive oral formulations are designed primarily to achieve which advantage?

• Rapid gastric emptying
• Increased luminal degradation by enzymes
• Prolonged residence time at absorption site to enhance uptake
• Reduction of drug solubility

Correct Answer: Prolonged residence time at absorption site to enhance uptake

Q26. Grapefruit juice co‑administration commonly increases oral bioavailability of certain drugs by what mechanism?

• Inducing P‑glycoprotein expression
• Inhibiting CYP3A4 in the intestinal wall
• Binding drugs to dietary fiber
• Accelerating gastric emptying

Correct Answer: Inhibiting CYP3A4 in the intestinal wall

Q27. Cyclodextrin complexation is used in oral formulations to improve absorption by which mechanism?

• Converting drug into prodrug
• Forming inclusion complexes to increase aqueous solubility
• Blocking intestinal transporters permanently
• Increasing intestinal pH

Correct Answer: Forming inclusion complexes to increase aqueous solubility

Q28. Which region of the GIT has the highest perfusion and thus favors rapid systemic uptake of absorbed drugs?

• Stomach
• Small intestine
• Colon
• Esophagus

Correct Answer: Small intestine

Q29. In elderly patients, which physiological change commonly affects oral drug absorption?

• Increased gastric acid secretion
• Faster intestinal transit time
• Reduced gastric motility and altered pH, potentially changing dissolution and absorption
• Markedly increased first‑pass hepatic metabolism

Correct Answer: Reduced gastric motility and altered pH, potentially changing dissolution and absorption

Q30. Neonates typically have higher gastric pH than adults; how does this affect absorption of weak acidic drugs?

• Increases absorption because weak acids are more ionized
• Decreases absorption because weak acids are less unionized in higher pH
• No effect on absorption
• Converts weak acids into bases

Correct Answer: Decreases absorption because weak acids are less unionized in higher pH

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