Basic concepts of sustained and controlled release MCQs With Answer

Basic concepts of sustained and controlled release MCQs With Answer help M.Pharm students master the foundational principles of designing dosage forms that prolong or regulate drug delivery. This quiz focuses on key distinctions between sustained and controlled release, kinetic models (zero-order, Higuchi, Korsmeyer–Peppas, Hixson–Crowell), diffusional and erosion mechanisms, polymer–drug interactions, and design considerations such as porosity, tortuosity, sink conditions, burst effect, dosage form risks, and IVIVC. You will also test your understanding of osmotic systems, reservoir vs matrix designs, gastroretentive approaches, and clinical pharmacokinetic implications like flip–flop kinetics and loading/maintenance strategies. Each question targets decision-making and mechanistic reasoning expected at the M.Pharm level in Drug Delivery Systems (MPH 102T).

Q1. Which statement best differentiates sustained-release from controlled-release dosage forms?

• Sustained-release aims for a constant, zero-order input over time independent of physiological variables
• Sustained-release reduces dosing frequency by prolonging release without necessarily maintaining a constant rate
• Controlled-release simply slows disintegration and dissolution without affecting plasma level fluctuations
• Controlled-release products always rely on chemical degradation of the polymer matrix

Correct Answer: Sustained-release reduces dosing frequency by prolonging release without necessarily maintaining a constant rate

Q2. A truly controlled-release system ideally exhibits which kinetic behavior?

• Zero-order release rate, independent of remaining drug concentration
• First-order release rate, proportional to remaining drug concentration
• Second-order release, dependent on square of concentration
• Auto-catalytic release dependent on polymer degradation only

Correct Answer: Zero-order release rate, independent of remaining drug concentration

Q3. For a non-erodible, diffusion-controlled matrix, which model most appropriately describes the cumulative drug released as a function of the square root of time?

• First-order model
• Higuchi model
• Korsmeyer–Peppas model (power-law) with n ≠ 0.5
• Hixson–Crowell cube-root model

Correct Answer: Higuchi model

Q4. In the Korsmeyer–Peppas model for a planar matrix, which diffusional exponent (n) indicates Case II (zero-order) transport?

• n = 0.5
• n ≈ 0.45
• n = 1.0
• 0.5 < n < 1.0

Correct Answer: n = 1.0

Q5. The permeability (P) of a drug across a polymeric membrane in a reservoir system is primarily governed by:

• Only the membrane thickness
• The product of drug partition coefficient (K) and diffusivity (D) divided by membrane thickness (h)
• Only the drug’s aqueous solubility in the donor phase
• Only the polymer glass transition temperature (Tg)

Correct Answer: The product of drug partition coefficient (K) and diffusivity (D) divided by membrane thickness (h)

Q6. Which strategy is most appropriate to minimize the initial burst release from a hydrophilic matrix tablet?

• Increase drug particle size to reduce surface area
• Seal-coat the tablet with a thin rate-controlling polymer layer to cover surface drug
• Use a highly water-soluble filler to speed gel layer formation
• Increase agitation speed during dissolution testing

Correct Answer: Seal-coat the tablet with a thin rate-controlling polymer layer to cover surface drug

Q7. Which statement best describes osmotic pump–based oral controlled-release systems?

• Release rate is driven primarily by GI pH variations
• Release rate is primarily driven by an osmotic pressure gradient and can approximate zero-order
• They require drug–polymer chemical bonding to function
• They are unsuitable for water-soluble drugs

Correct Answer: Release rate is primarily driven by an osmotic pressure gradient and can approximate zero-order

Q8. Which dosage form type is most prone to dose dumping upon membrane failure?

• Monolithic (matrix) system
• Reservoir system with a rate-controlling membrane
• Enteric-coated immediate-release tablet
• Delayed-release multiparticulates

Correct Answer: Reservoir system with a rate-controlling membrane

Q9. A Level A in vitro–in vivo correlation (IVIVC) is best defined as:

• A rank-order relationship between formulations’ dissolution rates and Cmax
• A point-to-point relationship between in vitro dissolution and the in vivo drug input rate or fraction absorbed
• A correlation limited to a single time point dissolution value and AUC
• A correlation using animal data extrapolated to humans

Correct Answer: A point-to-point relationship between in vitro dissolution and the in vivo drug input rate or fraction absorbed

Q10. Flip–flop kinetics in oral controlled-release products occurs when:

• The elimination rate constant exceeds the absorption rate constant, making the terminal half-life reflect absorption
• The absorption rate constant exceeds the elimination rate constant, making the terminal half-life reflect elimination
• Both absorption and elimination rate constants are equal
• Bioavailability is zero due to presystemic metabolism

Correct Answer: The elimination rate constant exceeds the absorption rate constant, making the terminal half-life reflect absorption

Q11. For oral sustained-release design, the most suitable candidates are typically:

• BCS Class I drugs with moderate dose and biological half-life of about 2–6 hours
• BCS Class IV drugs with very low solubility and permeability
• Highly potent drugs with half-life > 24 hours
• Very high dose, poorly soluble drugs with narrow therapeutic index

Correct Answer: BCS Class I drugs with moderate dose and biological half-life of about 2–6 hours

Q12. In dissolution/release testing of controlled-release products, “sink conditions” generally imply:

• Agitation speed is above 200 rpm
• The medium volume maintains drug concentration below 10–20% of saturation solubility throughout the test
• Use of a surfactant is mandatory
• The test is conducted at pH 1.2 only

Correct Answer: The medium volume maintains drug concentration below 10–20% of saturation solubility throughout the test

Q13. In porous matrices, which change most directly increases the Higuchi release constant?

• Decrease in porosity and increase in tortuosity
• Increase in porosity and decrease in tortuosity
• Increase in matrix thickness without altering porosity
• Decrease in drug solubility within the matrix

Correct Answer: Increase in porosity and decrease in tortuosity

Q14. Which polymer class is a classic example of surface-eroding materials used for controlled release?

• Poly(lactic-co-glycolic acid) (PLGA)
• Polyanhydrides
• Poly(ethylene-co-vinyl acetate) (EVA)
• Hydroxypropyl methylcellulose (HPMC)

Correct Answer: Polyanhydrides

Q15. The Hixson–Crowell cube-root model is most appropriate when drug release is controlled by:

• Diffusion through a non-eroding matrix with constant surface area
• Swelling-controlled relaxation of a polymer network
• Change in surface area and diameter of particles/tablets as they dissolve or erode
• Enzymatic degradation in the GI tract

Correct Answer: Change in surface area and diameter of particles/tablets as they dissolve or erode

Q16. To achieve rapid onset followed by prolonged action in a single oral dosage form, the preferred design is:

• Pure sustained-release matrix without any immediate-release component
• Biphasic system combining an immediate-release loading fraction with a sustained-release maintenance fraction
• Enteric-coated immediate-release core
• Multiple immediate-release doses taken sequentially

Correct Answer: Biphasic system combining an immediate-release loading fraction with a sustained-release maintenance fraction

Q17. For a membrane-controlled transdermal system, the steady-state flux is primarily proportional to:

• The square of drug concentration in the skin
• Patch area and membrane permeability, assuming a constant donor activity
• Skin blood flow only
• Ambient humidity

Correct Answer: Patch area and membrane permeability, assuming a constant donor activity

Q18. Gastroretentive sustained-release systems are most beneficial for drugs that:

• Are absorbed uniformly throughout the entire colon only
• Have a narrow absorption window in the stomach or proximal small intestine
• Exhibit pH-independent solubility
• Are unstable in gastric fluid

Correct Answer: Have a narrow absorption window in the stomach or proximal small intestine

Q19. Incorporating a pH modifier (e.g., citric acid) into a hydrophilic matrix of a weakly basic drug primarily aims to:

• Decrease drug solubility in the gel layer
• Maintain an acidic microenvironment to enhance drug solubility and sustain release
• Increase polymer crosslinking
• Prevent swelling of the matrix

Correct Answer: Maintain an acidic microenvironment to enhance drug solubility and sustain release

Q20. The primary clinical advantage of a true controlled-release profile over simple sustained-release is:

• Higher peak concentrations to ensure rapid onset
• Maintaining plasma levels within the therapeutic window with minimal peak–trough fluctuation
• Complete independence from gastrointestinal conditions
• Reduced first-pass metabolism

Correct Answer: Maintaining plasma levels within the therapeutic window with minimal peak–trough fluctuation

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