pH-activated drug delivery systems MCQs With Answer

Introduction

pH-activated drug delivery systems are designed to sense physiological pH differences across the gastrointestinal tract, tumor microenvironment, or intracellular compartments, and to release drug precisely where it is needed. For M. Pharm students, mastering polymer selection, linker chemistry, dissolution testing, and mechanistic models is essential to translate this concept into robust dosage forms. This quiz focuses on critical ideas such as ionizable polymer pKa, enteric coating thresholds (Eudragit, HPMCP/HPMCAS), acid-labile linkers (hydrazone, acetal), proton-sponge effect, endosomal escape, and biorelevant dissolution protocols. Tackle these MCQs to solidify your understanding of design variables, quality attributes, and evaluation methods that underpin pH-responsive formulations in both oral and nanocarrier-based drug delivery.

Q1. Which statement best describes a pH-activated drug delivery system?

• It uses environmental pH changes to trigger a physicochemical transition that modulates drug release
• It relies exclusively on enzymatic degradation to release drug
• It delivers drug at a constant rate regardless of physiological conditions
• It requires external magnetic fields to initiate drug release

Correct Answer: It uses environmental pH changes to trigger a physicochemical transition that modulates drug release

Q2. The most critical parameter when selecting an ionizable polymer for pH-triggered release is:

• Polymer glass transition temperature (Tg)
• Polymer pKa relative to the target site pH
• Polymer color and visual clarity
• Crystallinity index by XRD

Correct Answer: Polymer pKa relative to the target site pH

Q3. Which linker is classically used for acid-triggered cleavage in mildly acidic environments (e.g., tumor/endosome)?

• Hydrazone linkage
• Disulfide linkage
• Azo linkage
• Ether linkage

Correct Answer: Hydrazone linkage

Q4. Eudragit L (e.g., L100) is designed to dissolve and release drug at approximately:

• pH ≥ 5.0
• pH ≥ 6.0
• pH ≥ 7.0
• pH ≥ 8.0

Correct Answer: pH ≥ 6.0

Q5. Which in vitro protocol best demonstrates the gastric protection of an enteric-coated dosage form?

• Immediate release in water (pH ~7) with no acid stage
• No release in 0.1 N HCl for 2 hours followed by release in pH 6.8 phosphate buffer
• Release only in pH 4.5 acetate buffer
• Release only in pH 8.0 borate buffer

Correct Answer: No release in 0.1 N HCl for 2 hours followed by release in pH 6.8 phosphate buffer

Q6. Which pH profile correctly reflects tumor extracellular pH versus normal tissue?

• Tumor pHe 7.6–7.8; normal tissue ~7.0
• Tumor pHe 6.5–6.9; normal tissue ~7.4
• Tumor pHe 5.0–5.5; normal tissue ~6.5
• Tumor pHe 7.4; normal tissue 6.5–6.9

Correct Answer: Tumor pHe 6.5–6.9; normal tissue ~7.4

Q7. Which intracellular pH gradient is typically exploited for endosomal-triggered release?

• Endosome pH 7.4; lysosome pH 7.0
• Endosome pH 5.0–6.0; lysosome pH 4.5–5.0
• Endosome pH 8.0; lysosome pH 7.4
• Endosome pH 6.8–7.0; lysosome pH 6.5–6.8

Correct Answer: Endosome pH 5.0–6.0; lysosome pH 4.5–5.0

Q8. Which polymer is best known for the “proton sponge” effect facilitating endosomal escape?

• Poly(lactic-co-glycolic acid) (PLGA)
• Polyethylene glycol (PEG)
• Polyethylenimine (PEI)
• Polycaprolactone (PCL)

Correct Answer: Polyethylenimine (PEI)

Q9. A common pH-sensitive liposome formulation uses:

• DOPE with cholesteryl hemisuccinate (CHEMS)
• DSPC with high cholesterol content only
• DPPC with sphingomyelin only
• POPC with tocopherol only

Correct Answer: DOPE with cholesteryl hemisuccinate (CHEMS)

Q10. Which reagent is widely used to create charge-reversal coatings that detach in mildly acidic tumor pH?

• Succinic anhydride
• 2,3-Dimethylmaleic anhydride (DMMA)
• Glutaraldehyde
• EDC/NHS carbodiimide

Correct Answer: 2,3-Dimethylmaleic anhydride (DMMA)

Q11. Which HPMCAS grade is most suitable when release should begin at pH ≥ 6.5?

• HPMCAS-LG (dissolves at pH ≥ 5.5)
• HPMCAS-MG (dissolves at pH ≥ 6.0)
• HPMCAS-HG (dissolves at pH ≥ 6.5)
• HPMC (non-enteric, pH-independent)

Correct Answer: HPMCAS-HG (dissolves at pH ≥ 6.5)

Q12. For colon targeting based on pH, which polymer is classically selected?

• Eudragit S100 (dissolves at pH ≥ 7.0)
• Eudragit E (soluble in gastric pH)
• Gelatin (enzymatically degradable)
• Ethylcellulose (water-insoluble, non-ionizable)

Correct Answer: Eudragit S100 (dissolves at pH ≥ 7.0)

Q13. Regarding weakly basic drugs in acidic microenvironments, which statement is most accurate?

• They become unionized and permeate membranes more readily
• They become protonated and can be trapped in acidic compartments, reducing cytosolic penetration
• They precipitate irreversibly at neutral pH
• They undergo redox-triggered cleavage

Correct Answer: They become protonated and can be trapped in acidic compartments, reducing cytosolic penetration

Q14. Increasing enteric coating weight gain on pellets generally:

• Decreases acid resistance and advances release onset
• Has no effect on lag time or release pH
• Increases acid resistance and prolongs lag time before release
• Makes the system osmotic rather than pH-dependent

Correct Answer: Increases acid resistance and prolongs lag time before release

Q15. Which kinetic model is most appropriate to empirically describe release from swelling, pH-responsive polymer matrices?

• Zero-order model
• Higuchi diffusion model
• Korsmeyer–Peppas power law
• Hixson–Crowell cube root model

Correct Answer: Korsmeyer–Peppas power law

Q16. A suitable method to confirm pH-triggered cleavage of an acid-labile linker in vitro is:

• Measuring zeta potential only at pH 7.4
• HPLC quantification of drug released under pH 5.0 versus pH 7.4 conditions
• DSC thermogram comparison before and after hydration
• Optical microscopy of dry particles

Correct Answer: HPLC quantification of drug released under pH 5.0 versus pH 7.4 conditions

Q17. In pH-sensitive liposomes based on DOPE/CHEMS, endosomal acidification triggers release primarily because:

• CHEMS becomes deprotonated, stabilizing the bilayer
• DOPE converts to a hexagonal HII phase upon CHEMS protonation, destabilizing the membrane
• PEG sheds from the surface due to base-catalyzed hydrolysis
• Cholesterol crystallizes at low pH

Correct Answer: DOPE converts to a hexagonal HII phase upon CHEMS protonation, destabilizing the membrane

Q18. Which is a critical quality attribute (CQA) for enteric-coated multiparticulates enabling reliable pH-triggered release?

• Coating weight gain and uniformity across pellets
• Pellet color uniformity under daylight
• Fragrance masking agent concentration
• Primary container color

Correct Answer: Coating weight gain and uniformity across pellets

Q19. For biorelevant dissolution of pH-activated oral formulations in the fed state, which medium and pH are most appropriate?

• FaSSIF, pH ~6.5
• FeSSIF, pH ~5.0
• SGF, pH 1.2 without enzymes
• PBS, pH 7.4 only

Correct Answer: FeSSIF, pH ~5.0

Q20. Which marketed example illustrates pH-triggered colonic release using a methacrylic acid copolymer?

• Mesalamine delayed-release tablets coated with Eudragit S (e.g., Asacol)
• Doxycycline immediate-release capsules
• Insulin glargine injection
• Liposomal doxorubicin injection (temperature-responsive)

Correct Answer: Mesalamine delayed-release tablets coated with Eudragit S (e.g., Asacol)

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