Factors Affecting GIT Absorption MCQs With Answer

Factors Affecting GIT Absorption MCQs With Answer

This quiz set focuses on the physicochemical, physiological and formulation-related factors that influence gastrointestinal (GIT) drug absorption — a core area in Advanced Biopharmaceutics & Pharmacokinetics for M.Pharm students. Questions probe mechanisms such as ionization (pKa/pH), permeability, solubility, dissolution rate, gastric emptying, intestinal transit, first‑pass metabolism, transporters (e.g., P‑gp), enzymes (e.g., CYP3A4), and formulation strategies (e.g., salt forms, particle size reduction, excipients). Emphasis is on understanding how these factors interact to determine bioavailability and therapeutic effect. The set is designed to test conceptual depth, application of equations (Henderson‑Hasselbalch, Fick’s law), and critical thinking about formulation and clinical scenarios.

Q1. Which statement best explains why a weakly basic drug with pKa 6.5 exhibits higher absorption in the proximal small intestine than in the stomach?

• Proximal small intestine has lower surface area than stomach, reducing first‑pass
• pH in proximal small intestine is closer to the drug pKa, favoring unionized form and higher membrane permeability
• Gastric mucus binds basic drugs selectively, preventing absorption
• Gastric emptying concentrates the drug, reducing absorption

Correct Answer: pH in proximal small intestine is closer to the drug pKa, favoring unionized form and higher membrane permeability

Q2. According to the pH‑partition hypothesis, which factor most directly increases passive transcellular absorption of an acidic drug?

• Increasing luminal pH above the drug pKa, increasing the fraction unionized
• Decreasing blood pH to trap the drug in enterocytes
• Adding a P‑gp inhibitor to the formulation
• Increasing intestinal motility to reduce residence time

Correct Answer: Increasing luminal pH above the drug pKa, increasing the fraction unionized

Q3. Which of the following represents the most important physicochemical property determining transcellular diffusion across enterocyte membranes?

• Aqueous solubility at gastric pH
• Lipophilicity (log P or log D) and degree of ionization
• Particle morphology observed by SEM
• Binding affinity to plasma proteins

Correct Answer: Lipophilicity (log P or log D) and degree of ionization

Q4. How does the unstirred water layer (UWL) adjacent to the intestinal epithelium affect absorption of a poorly soluble, highly lipophilic drug?

• UWL increases dissolution rate, enhancing absorption
• UWL provides a diffusion barrier that can limit flux of lipophilic molecules, especially for low solubility drugs
• UWL actively transports drugs via carrier proteins
• UWL promotes enzymatic metabolism of lipophilic drugs

Correct Answer: UWL provides a diffusion barrier that can limit flux of lipophilic molecules, especially for low solubility drugs

Q5. Which formulation strategy most effectively increases the dissolution rate of a poorly water‑soluble crystalline drug in the GIT?

• Forming a salt of the drug with a lipophilic counterion
• Reducing particle size to nano/micron scale to increase surface area
• Encouraging crystallization during manufacturing
• Administering with a fatty meal to slow gastric emptying

Correct Answer: Reducing particle size to nano/micron scale to increase surface area

Q6. Which of the following most increases the extent of first‑pass hepatic metabolism for an orally administered drug?

• High solubility leading to rapid absorption into systemic circulation
• High hepatic extraction ratio and rapid portal blood delivery from the intestine
• Formulating as a prodrug designed to bypass intestinal enzymes
• Using enteric coating to delay drug release until the colon

Correct Answer: High hepatic extraction ratio and rapid portal blood delivery from the intestine

Q7. Which intestinal region provides the largest surface area and is therefore often the primary site for drug absorption?

• Stomach
• Duodenum and jejunum (proximal small intestine)
• Ileum only
• Colon

Correct Answer: Duodenum and jejunum (proximal small intestine)

Q8. How does gastric emptying rate influence the absorption of a highly soluble immediate‑release tablet?

• Slower gastric emptying generally increases the rate of absorption because dissolution is improved in stomach
• Faster gastric emptying typically accelerates delivery to the small intestine and can increase absorption rate for drugs absorbed primarily in the intestine
• Gastric emptying has no effect on absorption of highly soluble drugs
• Faster gastric emptying always decreases total bioavailability by enhancing first‑pass metabolism

Correct Answer: Faster gastric emptying typically accelerates delivery to the small intestine and can increase absorption rate for drugs absorbed primarily in the intestine

Q9. Which transporter is most commonly implicated in limiting oral absorption by effluxing drugs back into the intestinal lumen?

• OATP1B1
• P‑glycoprotein (P‑gp, MDR1)
• PEPT1 (peptide transporter)
• GLUT2 (glucose transporter)

Correct Answer: P‑glycoprotein (P‑gp, MDR1)

Q10. Co‑administration of a calcium supplement reduces the absorption of which class of antibiotics due to chelation in the GIT?

• Fluoroquinolones and tetracyclines
• Beta‑lactams
• Macrolides
• Aminoglycosides

Correct Answer: Fluoroquinolones and tetracyclines

Q11. Which kinetic expression best describes steady‑state passive diffusion across a membrane where concentration gradient is the driving force?

• Michealis–Menten equation
• Henderson‑Hasselbalch equation
• Fick’s first law of diffusion
• Arrhenius equation

Correct Answer: Fick’s first law of diffusion

Q12. Enterohepatic recirculation can prolong plasma half‑life of some drugs. Which process is essential for this phenomenon?

• Renal tubular secretion followed by reabsorption
• Biliary excretion of drug or conjugate into intestine followed by deconjugation and reabsorption
• Direct absorption in the stomach only
• Metabolism exclusively by CYP2D6

Correct Answer: Biliary excretion of drug or conjugate into intestine followed by deconjugation and reabsorption

Q13. Which change in formulation is most likely to reduce variability in absorption caused by food effects for a lipophilic drug?

• Convert to an immediate‑release crystalline powder
• Develop a lipid‑based formulation (self‑emulsifying drug delivery system) to maintain solubilization independent of bile secretion
• Increase tablet size to delay disintegration
• Remove any surfactants to avoid interactions with dietary fats

Correct Answer: Develop a lipid‑based formulation (self‑emulsifying drug delivery system) to maintain solubilization independent of bile secretion

Q14. Which physiological change in elderly patients is most likely to decrease oral drug absorption?

• Increased hepatic blood flow enhancing first‑pass effect
• Reduced gastric acid secretion and slower gastric emptying, potentially altering dissolution of certain drugs
• Marked increase in intestinal surface area
• Higher expression of intestinal CYP3A4 enzymes compared to young adults

Correct Answer: Reduced gastric acid secretion and slower gastric emptying, potentially altering dissolution of certain drugs

Q15. Why can prodrugs be used to enhance oral absorption of poorly permeable drugs?

• Prodrugs always increase aqueous solubility and therefore absorption
• Prodrugs temporarily mask polar functional groups to increase lipophilicity and membrane permeation, then convert to active drug in vivo
• Prodrugs prevent hepatic metabolism completely
• Prodrugs increase gastric residence time by forming gels

Correct Answer: Prodrugs temporarily mask polar functional groups to increase lipophilicity and membrane permeation, then convert to active drug in vivo

Q16. Which excipient is commonly used to enhance wetting and dissolution of hydrophobic drug particles in oral dosage forms?

• Magnesium stearate as the sole excipient
• Surfactants such as polysorbates or sodium lauryl sulfate
• Starch as a disintegrant only
• Microcrystalline cellulose to reduce wettability

Correct Answer: Surfactants such as polysorbates or sodium lauryl sulfate

Q17. Which of the following best explains why a highly permeable, highly soluble (BCS Class I) drug shows low oral bioavailability?

• Formulation excipients always cause precipitation in the GIT
• Extensive presystemic (first‑pass) hepatic or intestinal metabolism can markedly reduce bioavailability despite good solubility and permeability
• High permeability prevents drug from dissolving
• BCS Class I drugs are inherently unstable and degrade immediately in gastric acid

Correct Answer: Extensive presystemic (first‑pass) hepatic or intestinal metabolism can markedly reduce bioavailability despite good solubility and permeability

Q18. Which factor most contributes to regional differences in transporter and metabolic enzyme expression along the intestine?

• Uniform blood flow and pH throughout the GIT
• Variation in enterocyte differentiation, luminal exposure, and local microenvironment leading to different expression of CYPs and transporters
• Presence of gastric glands in the colon
• Constant mucus thickness from duodenum to colon

Correct Answer: Variation in enterocyte differentiation, luminal exposure, and local microenvironment leading to different expression of CYPs and transporters

Q19. Which experimental method provides direct quantitative measurement of intestinal permeability in vitro for drug screening?

• Caco‑2 cell monolayer assay measuring apparent permeability (Papp)
• Disintegration test using USP apparatus
• Polarographic titration of drug pKa
• HPLC assay of dissolution media only

Correct Answer: Caco‑2 cell monolayer assay measuring apparent permeability (Papp)

Q20. How does formation of a supersaturated solution in the intestinal lumen affect oral absorption of a poorly soluble drug?

• Supersaturation reduces the concentration gradient and decreases absorption
• Supersaturation temporarily increases free drug concentration and can enhance absorption rate and extent unless precipitation occurs
• Supersaturated systems are irrelevant to absorption kinetics
• Supersaturation always leads to complete drug degradation by luminal enzymes

Correct Answer: Supersaturation temporarily increases free drug concentration and can enhance absorption rate and extent unless precipitation occurs

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