Factors influencing drug absorption MCQs With Answer

Introduction: This quiz set on Factors Influencing Drug Absorption is designed for M.Pharm students preparing for Advanced Biopharmaceutics & Pharmacokinetics (MPH 202T). It covers core principles that determine how much and how fast a drug reaches systemic circulation — including physicochemical properties (pKa, lipophilicity, molecular size), formulation variables (particle size, salt form, excipients, coatings), physiological influences (GI pH, gastric emptying, intestinal enzymes, transporters like P‑gp), and special pathways (lymphatic uptake, first‑pass metabolism). The 20 MCQs emphasize mechanistic understanding and application to formulation and clinical scenarios, helping you strengthen problem solving for exams and research-focused tasks.

Q1. Which statement best reflects the pH partition hypothesis regarding oral drug absorption?

• Ionized drugs cross lipid membranes more readily than non‑ionized drugs
• Only hydrophilic drugs are absorbed from the gastrointestinal tract
• Non‑ionized form of a drug is generally more permeable across biological membranes
• Absorption is independent of the drug’s degree of ionization

Correct Answer: Non‑ionized form of a drug is generally more permeable across biological membranes

Q2. A weak acid drug has pKa 4.5. In the stomach at pH 1.5, which form predominates and what is the implication for absorption?

• Ionized form predominates; absorption is increased
• Non‑ionized form predominates; absorption is favored in the stomach
• Ionized form predominates; absorption is favored in the intestine
• Non‑ionized form predominates; absorption is negligible because stomach surface area is too small

Correct Answer: Non‑ionized form predominates; absorption is favored in the stomach

Q3. Which physicochemical property is most directly correlated with passive transcellular permeability across enterocytes?

• High aqueous solubility
• High polar surface area
• High lipophilicity (log P)
• High melting point

Correct Answer: High lipophilicity (log P)

Q4. According to the Noyes‑Whitney equation, which change will increase the dissolution rate of a poorly soluble solid drug?

• Decrease the diffusion coefficient
• Decrease the surface area of the particles
• Increase the thickness of the unstirred diffusion layer
• Reduce particle size to increase surface area

Correct Answer: Reduce particle size to increase surface area

Q5. A drug classified as BCS Class III is expected to have which characteristics?

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

Correct Answer: High solubility, low permeability

Q6. Micronization of a drug powder primarily improves oral absorption by which mechanism?

• Increasing the drug’s intrinsic permeability across membranes
• Enhancing chemical stability in gastric acid
• Increasing apparent solubility by reducing particle size and increasing surface area
• Preventing first‑pass metabolism

Correct Answer: Increasing apparent solubility by reducing particle size and increasing surface area

Q7. A high‑fat meal commonly affects the oral absorption of highly lipophilic drugs by:

• Decreasing bile secretion and reducing solubilization
• Delaying gastric emptying but increasing lymphatic transport and solubilization via bile salts
• Destroying the drug in the stomach leading to lower bioavailability
• Enhancing first‑pass hepatic metabolism and reducing absorption

Correct Answer: Delaying gastric emptying but increasing lymphatic transport and solubilization via bile salts

Q8. Which organ is the principal site of first‑pass metabolism affecting oral bioavailability?

• Kidney
• Liver
• Lungs
• Spleen

Correct Answer: Liver

Q9. P‑glycoprotein (P‑gp) expressed on the apical membrane of enterocytes primarily affects drug absorption by:

• Facilitating passive diffusion into enterocytes
• Actively transporting drugs from blood into enterocytes
• Effluxing substrate drugs back into the intestinal lumen, reducing net absorption
• Increasing drug solubility in the lumen

Correct Answer: Effluxing substrate drugs back into the intestinal lumen, reducing net absorption

Q10. The unstirred water layer at the intestinal mucosa impacts drug absorption because it:

• Acts as a metabolic enzyme barrier
• Serves as an additional diffusion barrier slowing drug transfer to the epithelium
• Enhances absorption by concentrating drug near the membrane
• Is only relevant for parenteral administration

Correct Answer: Serves as an additional diffusion barrier slowing drug transfer to the epithelium

Q11. Which formulation strategy is commonly used to enhance paracellular absorption of hydrophilic drugs?

• Use of lipophilic prodrugs
• Incorporation of permeation enhancers that transiently open tight junctions
• Increasing particle size to reduce dissolution rate
• Adding efflux transporter substrates to compete with the drug

Correct Answer: Incorporation of permeation enhancers that transiently open tight junctions

Q12. Conversion of a drug to a suitable salt form typically improves oral absorption by:

• Always increasing lipophilicity to favor membrane permeation
• Altering solubility and dissolution rate without changing intrinsic membrane permeability
• Eliminating the need for metabolic activation
• Preventing renal excretion

Correct Answer: Altering solubility and dissolution rate without changing intrinsic membrane permeability

Q13. Designing a lipophilic prodrug is a common tactic to improve absorption because it:

• Increases aqueous solubility of the parent drug
• Reduces passive diffusion across membranes
• Enhances membrane permeation and can be cleaved in vivo to release the active drug
• Directly inhibits hepatic enzymes to avoid first‑pass

Correct Answer: Enhances membrane permeation and can be cleaved in vivo to release the active drug

Q14. A delayed gastric emptying would most likely cause which change in the oral pharmacokinetic profile of a rapidly absorbed tablet?

• Earlier Tmax and increased Cmax
• Delayed Tmax and possibly reduced Cmax
• No change in Tmax but increased bioavailability
• Immediate release of drug in the stomach with unchanged absorption

Correct Answer: Delayed Tmax and possibly reduced Cmax

Q15. Lymphatic transport of orally administered drugs is most favorable for molecules that are:

• Highly polar and low molecular weight
• Hydrophilic salts with log P < 0
• Highly lipophilic, often with log P > 5 and solubility in long‑chain triglycerides
• Strongly ionized at physiological pH

Correct Answer: Highly lipophilic, often with log P > 5 and solubility in long‑chain triglycerides

Q16. Enteric coating of an oral dosage form is primarily used to:

• Enhance dissolution in the stomach
• Mask bitter taste when placed under the tongue
• Protect acid‑labile drugs from gastric acid and delay release until the intestine
• Increase first‑pass metabolism

Correct Answer: Protect acid‑labile drugs from gastric acid and delay release until the intestine

Q17. Bile salts enhance absorption of poorly water‑soluble lipophilic drugs mainly by:

• Decreasing intestinal transit time
• Forming micelles that solubilize lipophilic drugs and increase their apparent solubility
• Converting drugs into ionized forms
• Inhibiting intestinal enzymes to prevent metabolism

Correct Answer: Forming micelles that solubilize lipophilic drugs and increase their apparent solubility

Q18. Which disease state is most likely to reduce oral drug absorption due to decreased surface area and enzymatic activity?

• Short bowel syndrome
• Renal failure
• Osteoarthritis
• Otitis media

Correct Answer: Short bowel syndrome

Q19. Intestinal CYP3A4 can limit oral bioavailability of certain drugs by:

• Enhancing passive diffusion across enterocytes
• Metabolizing drugs before they reach the portal circulation, contributing to presystemic clearance
• Acting as an efflux transporter to pump drugs into blood
• Forming micelles with drugs to improve solubility

Correct Answer: Metabolizing drugs before they reach the portal circulation, contributing to presystemic clearance

Q20. According to Fick’s first law of diffusion, the flux (J) of a drug across a membrane is directly proportional to which of the following?

• Membrane thickness
• Concentration gradient across the membrane
• Molecular weight only, independent of concentration
• Viscosity of the dosage form only

Correct Answer: Concentration gradient across the membrane

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