Introduction: The absorption of drugs is a central topic in pharmacokinetics and a critical subject for B. Pharm students. Understanding mechanisms such as passive diffusion, facilitated and active transport, and transcellular versus paracellular pathways helps predict drug bioavailability and onset of action. Key concepts include pH-partition theory, pKa, lipid solubility, surface area, blood flow, first-pass metabolism, P-glycoprotein efflux, and formulation strategies like enteric coatings or prodrugs. Mastery of these factors aids rational dosage form design and therapeutic optimization. This set of focused MCQs emphasizes core principles, calculation-based problems, and clinical implications to reinforce learning. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which mechanism primarily explains how weakly acidic drugs are absorbed from the stomach?
- Active transport via carrier proteins
- pH-partitioning leading to unionized form in acidic environment
- Paracellular diffusion through tight junctions
- Receptor-mediated endocytosis
Correct Answer: pH-partitioning leading to unionized form in acidic environment
Q2. According to Fick’s first law, which factor does NOT directly affect the passive diffusion rate of a drug?
- Concentration gradient across the membrane
- Surface area of the absorbing membrane
- Partition coefficient (lipid solubility)
- Plasma protein binding at the site of absorption
Correct Answer: Plasma protein binding at the site of absorption
Q3. The Henderson-Hasselbalch equation is used to relate drug ionization to pH and pKa. For a weak base, when pH < pKa, which form predominates?
- Unionized base predominates
- Ionized conjugate acid predominates
- Neutral zwitterion predominates
- Non-dissociated salt predominates
Correct Answer: Ionized conjugate acid predominates
Q4. Which statement best describes first-pass metabolism?
- Metabolism that occurs after systemic distribution to tissues
- Intestinal and hepatic metabolism reducing oral bioavailability before systemic circulation
- Elimination by the kidneys before the drug reaches the liver
- Metabolism occurring in the lungs for inhaled drugs
Correct Answer: Intestinal and hepatic metabolism reducing oral bioavailability before systemic circulation
Q5. Which of the following enhances lymphatic absorption of lipophilic drugs?
- Formulation as a hydrophilic salt
- Co-administration with a long-chain triglyceride or lipid-based formulation
- Low molecular weight and high water solubility
- Enteric coating that dissolves in the stomach
Correct Answer: Co-administration with a long-chain triglyceride or lipid-based formulation
Q6. Caco-2 cell monolayers are used experimentally to predict which property of drug candidates?
- Metabolic half-life in liver microsomes
- Permeability and intestinal absorption potential
- Plasma protein binding affinity
- Renal clearance rate
Correct Answer: Permeability and intestinal absorption potential
Q7. Which factor most increases the rate of gastric emptying and thereby can accelerate absorption of orally administered drugs?
- High-fat meal ingestion
- Anticholinergic medications
- Prokinetic agents like metoclopramide
- Opioid analgesics
Correct Answer: Prokinetic agents like metoclopramide
Q8. Bioavailability (F) of an orally administered drug is defined as:
- The fraction of the administered dose eliminated unchanged in urine
- The fraction of dose reaching systemic circulation unchanged compared to IV administration
- The time to reach maximum concentration (Tmax)
- The ratio of bound to unbound drug in plasma
Correct Answer: The fraction of dose reaching systemic circulation unchanged compared to IV administration
Q9. Which BCS (Biopharmaceutics Classification System) class describes drugs with high solubility but low permeability?
- Class I
- Class II
- Class III
- Class IV
Correct Answer: Class III
Q10. P-glycoprotein (P-gp) efflux in enterocytes primarily causes which effect on orally administered substrates?
- Increased passive diffusion across the apical membrane
- Enhanced absorption into systemic circulation
- Reduced intracellular accumulation and decreased oral bioavailability
- Conversion to more lipophilic metabolites
Correct Answer: Reduced intracellular accumulation and decreased oral bioavailability
Q11. Which formulation strategy is most appropriate to protect an acid-labile drug from stomach acid?
- Immediate release tablet
- Enteric-coated dosage form
- Chewable tablet
- Micronized powder for suspension
Correct Answer: Enteric-coated dosage form
Q12. For a weak acid with pKa 4.5, in which GI region will it be mostly unionized and favor absorption?
- Stomach (pH ~1–3)
- Proximal small intestine (pH ~5–6)
- Distal small intestine (pH ~7–8)
- Colon (pH ~6–7)
Correct Answer: Stomach (pH ~1–3)
Q13. Which process is characteristic of transcellular absorption but NOT paracellular absorption?
- Movement through tight junctions
- Requirement for lipid solubility to cross cell membranes
- Passive diffusion driven by concentration gradients
- Dependence on pore size between cells
Correct Answer: Requirement for lipid solubility to cross cell membranes
Q14. Which change in disease state would most likely decrease oral drug absorption?
- Increased gastric emptying due to hyperthyroidism
- Short bowel syndrome with reduced absorptive surface area
- Enhanced intestinal blood flow after exercise
- Use of enteric-coated formulations
Correct Answer: Short bowel syndrome with reduced absorptive surface area
Q15. The rate-limiting step for absorption of a poorly soluble, highly permeable drug (BCS Class II) is typically:
- Membrane permeability across enterocytes
- Drug dissolution in gastrointestinal fluids
- First-pass hepatic metabolism
- Renal excretion
Correct Answer: Drug dissolution in gastrointestinal fluids
Q16. Which factor most directly reduces the oral bioavailability of a drug subjected to extensive hepatic first-pass metabolism?
- High fraction unbound in plasma
- High hepatic extraction ratio
- High aqueous solubility
- Rapid gastrointestinal transit time
Correct Answer: High hepatic extraction ratio
Q17. Which statement correctly describes the pH-partition hypothesis for absorption?
- Ionized drugs are always absorbed faster than unionized drugs
- Unionized form crosses lipid membranes more readily than ionized form
- pH does not influence the extent of drug absorption
- Only active transport determines absorption irrespective of ionization
Correct Answer: Unionized form crosses lipid membranes more readily than ionized form
Q18. In neonates, which physiological difference commonly affects drug absorption compared to adults?
- Higher gastric acid secretion leading to faster dissolution of basic drugs
- Lower gastric pH and slower gastric emptying altering ionization and absorption
- Greater intestinal surface area per body weight reducing absorption
- More mature P-gp activity enhancing efflux
Correct Answer: Lower gastric pH and slower gastric emptying altering ionization and absorption
Q19. Which analytical parameter is directly measured in an absolute bioavailability study comparing oral and IV administration?
- Comparative Tmax values only
- Ratio of AUC oral to AUC intravenous adjusted for dose
- Peak urinary excretion rates
- Plasma protein binding constants
Correct Answer: Ratio of AUC oral to AUC intravenous adjusted for dose
Q20. Which excipient is commonly used to enhance dissolution rate of poorly soluble drugs by increasing wetting?
- Magnesium stearate as a lubricant
- Sodium lauryl sulfate as a surfactant
- Enteric polymer like cellulose acetate phthalate
- Hydrophobic binder such as ethylcellulose
Correct Answer: Sodium lauryl sulfate as a surfactant
Q21. Which experimental observation suggests carrier-mediated intestinal absorption?
- Linear increase in uptake with concentration
- Saturable uptake at higher concentrations
- Equal absorption rates across structurally diverse molecules
- No effect of specific transporter inhibitors
Correct Answer: Saturable uptake at higher concentrations
Q22. A drug with high lipophilicity and molecular weight > 500 Da is most likely to be absorbed via which route?
- Passive transcellular diffusion across enterocytes
- Paracellular diffusion through tight junctions
- Lymphatic transport when formulated in lipid vehicles
- Rapid passive renal reabsorption
Correct Answer: Lymphatic transport when formulated in lipid vehicles
Q23. Food can affect drug absorption. Which scenario typically decreases the rate but may increase the extent of absorption?
- Administration of a hydrophilic drug with water on an empty stomach
- High-fat meal delaying gastric emptying but improving solubilization of lipophilic drug
- Taking an enteric-coated tablet with antacid
- Administering a prodrug that requires acidic activation
Correct Answer: High-fat meal delaying gastric emptying but improving solubilization of lipophilic drug
Q24. Which property of drug salts commonly improves oral absorption compared to the free acid/base?
- Decreased aqueous solubility
- Increased stability against hepatic enzymes
- Enhanced dissolution rate and solubility
- Higher plasma protein binding
Correct Answer: Enhanced dissolution rate and solubility
Q25. Which kinetic parameter describes the time to reach maximum plasma concentration after oral dosing?
- Cmax
- Tmax
- Half-life (t1/2)
- Volume of distribution (Vd)
Correct Answer: Tmax
Q26. Enteric-coated tablets are intended primarily to:
- Accelerate release in the stomach
- Prevent drug release in the stomach and release in the intestine
- Enhance sublingual absorption
- Increase renal excretion
Correct Answer: Prevent drug release in the stomach and release in the intestine
Q27. For a drug that is a P-gp substrate, co-administration with a P-gp inhibitor will most likely:
- Decrease systemic exposure
- Increase oral bioavailability and systemic exposure
- Have no effect on absorption or bioavailability
- Convert the drug into an inactive metabolite
Correct Answer: Increase oral bioavailability and systemic exposure
Q28. Which laboratory model is commonly used to assess intestinal permeability and transporter interactions in vitro?
- Hepatocyte suspension assay
- Caco-2 cell monolayer model
- Renal proximal tubule slices
- Plasma protein binding assay
Correct Answer: Caco-2 cell monolayer model
Q29. Which statement about prodrugs is true regarding absorption?
- Prodrugs always have lower bioavailability than parent drugs
- Prodrugs can enhance absorption by improving lipophilicity or stability
- Prodrugs are active molecules that do not require metabolic conversion
- Prodrugs only reduce first-pass metabolism without affecting absorption
Correct Answer: Prodrugs can enhance absorption by improving lipophilicity or stability
Q30. In bioequivalence studies, which parameter is commonly compared between test and reference products to assess similarity?
- Absolute urinary excretion only
- Area under the plasma concentration-time curve (AUC) and Cmax
- Drug melting point and pKa
- In vitro dissolution temperature
Correct Answer: Area under the plasma concentration-time curve (AUC) and Cmax
I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.
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