Bioavailability is a core pharmacokinetic parameter that defines the fraction of an administered dose reaching systemic circulation intact. For B. Pharm students, mastering its definition, objectives—such as assessing absorption, formulation performance and therapeutic equivalence—and clinical importance in dose design, drug development and regulatory approval is essential. Key concepts include routes of administration, absorption rate and extent, first‑pass metabolism, formulation factors, solubility, permeability and the Biopharmaceutics Classification System (BCS). Understanding measurement methods, AUC-based calculations and factors altering bioavailability aids rational dosing, formulation optimization and interpretation of bioequivalence studies. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. What is the standard definition of absolute bioavailability (F)?
- The fraction of a dose absorbed into portal circulation
- The fraction of a dose reaching systemic circulation compared to an IV dose
- The fraction of drug metabolized during absorption
- The time taken to reach maximum plasma concentration
Correct Answer: The fraction of a dose reaching systemic circulation compared to an IV dose
Q2. Which pharmacokinetic parameter is primarily used to calculate bioavailability from plasma data?
- Cmax (maximum plasma concentration)
- Tmax (time to Cmax)
- AUC (area under the plasma concentration‑time curve)
- t1/2 (elimination half‑life)
Correct Answer: AUC (area under the plasma concentration‑time curve)
Q3. How is absolute bioavailability (F) calculated for an oral dose?
- F = (AUCoral / AUCiv) × (Doseiv / Doseoral)
- F = (Cmax oral / Cmax iv) × 100
- F = Doseoral / Doseiv
- F = (Tmax oral / Tmax iv) × 100
Correct Answer: F = (AUCoral / AUCiv) × (Doseiv / Doseoral)
Q4. What does a bioavailability value of 0.6 indicate?
- 60% of the administered dose reaches systemic circulation
- 60% of the dose is excreted unchanged
- The drug has 60% protein binding
- The drug is 60% metabolized in plasma
Correct Answer: 60% of the administered dose reaches systemic circulation
Q5. Which factor most directly reduces oral bioavailability via first‑pass effect?
- High aqueous solubility
- Extensive hepatic metabolism before reaching systemic circulation
- Slow gastric emptying
- Low molecular weight
Correct Answer: Extensive hepatic metabolism before reaching systemic circulation
Q6. Relative bioavailability compares:
- Oral bioavailability of a drug to its IV bioavailability
- Different formulations or routes against a reference formulation
- Bioavailability in different species
- Total bioavailability across all routes
Correct Answer: Different formulations or routes against a reference formulation
Q7. AUC is proportional to which of the following (assuming linear kinetics)?
- Clearance divided by Dose
- Dose divided by Clearance
- Volume of distribution only
- Elimination half‑life only
Correct Answer: Dose divided by Clearance
Q8. Which experimental design is commonly used to assess bioequivalence between two oral formulations?
- Parallel group study with different subjects for each formulation
- Randomized crossover study in the same subjects
- Single timepoint sampling in different populations
- In vitro dissolution only
Correct Answer: Randomized crossover study in the same subjects
Q9. The Biopharmaceutics Classification System (BCS) categorizes drugs based on:
- Solubility and permeability
- Metabolic pathways and clearance
- Protein binding and half‑life
- Therapeutic index and potency
Correct Answer: Solubility and permeability
Q10. Which condition would most likely increase oral bioavailability?
- Induction of CYP450 enzymes in the liver
- Co‑administration of a P‑glycoprotein inhibitor in the gut
- Presence of a high first‑pass hepatic extraction ratio
- Gastric pH that reduces solubility
Correct Answer: Co‑administration of a P‑glycoprotein inhibitor in the gut
Q11. Which statement best distinguishes rate and extent of absorption?
- Rate is measured by AUC; extent is measured by Tmax
- Rate describes how quickly drug enters circulation (Tmax, Cmax); extent refers to total amount absorbed (AUC)
- Rate and extent are identical concepts
- Extent is determined by half‑life; rate is by volume of distribution
Correct Answer: Rate describes how quickly drug enters circulation (Tmax, Cmax); extent refers to total amount absorbed (AUC)
Q12. Which sampling consideration is critical when estimating AUC for bioavailability studies?
- Sampling only at Tmax is sufficient
- Frequent sampling during absorption and sufficient duration to capture elimination tail
- Sampling only after 24 hours is necessary
- No plasma sampling is needed if urine data are available
Correct Answer: Frequent sampling during absorption and sufficient duration to capture elimination tail
Q13. Which formulation strategy is most likely to improve bioavailability of a poorly soluble drug?
- Decrease surface area of drug particles
- Use solid dispersion or nanoparticle technology to enhance dissolution
- Increase crystal lattice energy
- Add a non‑dissolving filler
Correct Answer: Use solid dispersion or nanoparticle technology to enhance dissolution
Q14. Which clearance change would increase systemic bioavailability after non‑intravenous dosing?
- Increase in hepatic clearance
- Decrease in hepatic clearance
- Increase in renal clearance only
- No change in clearance affects bioavailability
Correct Answer: Decrease in hepatic clearance
Q15. What is the impact of high protein binding on bioavailability?
- It directly reduces the fraction absorbed from the gut
- It does not change the fraction reaching systemic circulation but affects free drug concentration and distribution
- It increases first‑pass metabolism
- It doubles the AUC for a given dose
Correct Answer: It does not change the fraction reaching systemic circulation but affects free drug concentration and distribution
Q16. In absolute bioavailability studies, why is an IV dose used as a reference?
- IV dosing avoids absorption and first‑pass losses, representing 100% systemic delivery
- IV dosing has slower onset and lower AUC
- IV dose is cheaper to administer
- IV dosing exaggerates first‑pass metabolism
Correct Answer: IV dosing avoids absorption and first‑pass losses, representing 100% systemic delivery
Q17. A drug shows zero oral bioavailability. Which is the most likely explanation?
- Complete absorption with no metabolism
- No absorption from the gastrointestinal tract or complete presystemic degradation
- High permeability and solubility
- Exclusively renal elimination after absorption
Correct Answer: No absorption from the gastrointestinal tract or complete presystemic degradation
Q18. Which parameter primarily reflects the rate of absorption?
- AUC0–∞
- Tmax and Cmax
- Volume of distribution
- Total clearance
Correct Answer: Tmax and Cmax
Q19. How can prodrugs improve bioavailability?
- By being more susceptible to intestinal efflux
- By being converted in vivo to active drug after improved absorption or reduced first‑pass metabolism
- By increasing hepatic metabolism
- By decreasing permeability across membranes
Correct Answer: By being converted in vivo to active drug after improved absorption or reduced first‑pass metabolism
Q20. Which analytical method is most commonly used to quantify plasma drug concentrations for bioavailability studies?
- UV visual inspection
- Validated LC‑MS/MS or HPLC methods
- pH titration
- Melting point determination
Correct Answer: Validated LC‑MS/MS or HPLC methods
Q21. Which statement about first‑pass hepatic extraction ratio (E) is true?
- E = 1 − (hepatic clearance / hepatic blood flow)
- E = hepatic clearance / hepatic blood flow
- E = fraction excreted unchanged in urine
- E = fraction bound to plasma proteins
Correct Answer: E = hepatic clearance / hepatic blood flow
Q22. During a bioequivalence study, the 90% confidence interval for the ratio of mean AUC of test to reference should typically fall within:
- 50–150%
- 80–125%
- 70–130%
- 90–110%
Correct Answer: 80–125%
Q23. Which population factor can significantly alter oral bioavailability?
- Genetic polymorphisms of metabolic enzymes (e.g., CYP2D6, CYP3A4)
- Shoe size of the patient
- Ambient room temperature only
- Blood type without any metabolic relevance
Correct Answer: Genetic polymorphisms of metabolic enzymes (e.g., CYP2D6, CYP3A4)
Q24. What is the effect of food that increases gastric pH on a weakly basic drug?
- Decreased solubility and decreased bioavailability
- Increased ionization and decreased absorption for a weak base, potentially reducing bioavailability
- No change in absorption
- Guaranteed increase in bioavailability
Correct Answer: Increased ionization and decreased absorption for a weak base, potentially reducing bioavailability
Q25. In noncompartmental analysis, AUC0–∞ is estimated by:
- Integrating concentration–time curve up to last measurable point and adding Clast/λz
- Only considering concentrations at Tmax
- Multiplying Cmax by Tmax
- Using half the Cmax value
Correct Answer: Integrating concentration–time curve up to last measurable point and adding Clast/λz
Q26. Which transporter expressed in intestinal epithelium can reduce oral bioavailability by effluxing drugs back into the lumen?
- OATP1B1
- P‑glycoprotein (P‑gp, ABCB1)
- Albumin
- CYP3A4 enzyme
Correct Answer: P‑glycoprotein (P‑gp, ABCB1)
Q27. Which scenario best describes relative bioavailability greater than 1 (or >100%)?
- The test formulation has lower exposure than reference
- The test formulation produces higher systemic exposure than the reference formulation
- Both formulations are identical
- AUC cannot exceed 100% by definition
Correct Answer: The test formulation produces higher systemic exposure than the reference formulation
Q28. Which of the following is a common objective of bioavailability studies in drug development?
- To determine the melting point of the active pharmaceutical ingredient
- To assess absorption characteristics, support dose selection and demonstrate bioequivalence
- To evaluate only the safety in animals
- To establish manufacturing cost
Correct Answer: To assess absorption characteristics, support dose selection and demonstrate bioequivalence
Q29. Which formulation change is least likely to affect bioavailability?
- Changing particle size to nanometer range
- Altering excipients that modify dissolution
- Changing tablet color coating without functional role
- Using lipid‑based formulation to enhance solubility
Correct Answer: Changing tablet color coating without functional role
Q30. For a drug with high hepatic extraction ratio, which factor predominantly determines its oral bioavailability?
- Fraction absorbed from gut only
- Hepatic blood flow and first‑pass extraction
- Renal clearance exclusively
- Volume of distribution only
Correct Answer: Hepatic blood flow and first‑pass extraction
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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